Baked Tuna Casserole Recipe: Creamy Mushroom and Peas in One Dish

This baked tuna casserole recipe delivers the comforting, creamy texture that makes it a classic—layered with tender tuna, mushrooms, and peas in a rich sauce. The secret lies in a velvety roux base that thickens beautifully while keeping the dish light enough for a weeknight dinner.

I’ve perfected this version to balance traditional flavors with modern convenience, whether you’re using gluten-free pasta or adding a spicy kick for depth.

The beauty of this dish is its simplicity: just a few key ingredients come together in one baking dish, making it ideal for busy evenings. Sautéed onions and mushrooms form the flavor foundation, while the tuna and peas add freshness.

The creamy sauce, made from a simple roux and milk mixture, ensures every bite is rich and satisfying without being heavy.

What you’ll end up with is a golden, bubbling casserole with tender pasta, flaky tuna, and perfectly cooked vegetables—all enveloped in that signature creamy sauce.

The aroma alone will have everyone at the table anticipating dinner, and the texture is just right: tender pasta, melt-in-your-mouth tuna, and a sauce that clings to every bite.

Serve this comforting dish with a side salad or crusty bread to soak up the extra sauce. It’s the kind of meal that feels like a hug in a dish, perfect for family dinners or potlucks. Let’s get started on this foolproof recipe!

Ingredients for baked tuna casserole

Pantry staples plus a few fresh touches—this casserole comes together fast.

The mushrooms are the flavor backbone here. Baby Bella or cremini from the store’s produce section slice fastest, but Wild Harvest at Trader Joe’s has the best pre-sliced mix—no chopping required. If you’re using dried mushrooms, soak them first and use the soaking liquid in the roux for extra depth. The tuna? Wild Planet or Starkist in water—skip the oil-packed kind, it’s too heavy. For the pasta, elbow macaroni holds its shape best after baking, but barley or gluten-free penne work too if you’ve got them.

No fresh thyme? Dried works at one-third the amount, but fresh has that bright aroma. Short on milk? Half-and-half or heavy cream makes it richer, but whole milk keeps it light. The roux is non-negotiable—it’s what makes the sauce velvety. Diamond Crystal flour gives the best texture, but any all-purpose works. For the cheese topping, Pepper Jack or Gruyère add a nice kick if you’re feeling fancy. And if you’re out of chicken broth? Vegetable broth works just as well—no one will notice.

This casserole reheats beautifully—honestly better the next day once everything melds. Keeps 4-5 days in the fridge, freezes for 3 months if you portion it into containers. I always make a double batch because it’s the kind of thing that disappears fast. Leftovers? Microwave with a splash of milk to revive the creaminess. And if you’ve got extra sauce, freeze it in ice cube trays for quick future meals.

Step-by-step instructions for creamy mushroom and peas in one dish

Here's how to make this comforting casserole with rich, velvety sauce and tender pasta.

Bring a large pot of salted water to a rolling boil. Add the 12 oz elbow macaroni and cook for 1 minute less than the package instructions suggest for al dente. You want the pasta to finish cooking in the oven, so it absorbs all that creamy sauce. Drain the pasta in a colander and set aside.

While the pasta cooks, I like to prep the other ingredients. This keeps everything moving smoothly and prevents that "waiting for water to boil" frustration. The key here is timing—you want the pasta to be perfectly tender when it hits the oven.

Heat 1 tablespoon olive oil in a large skillet over medium heat. Add the sliced 1 lb fresh mushrooms and the diced 1 whole yellow onion. Cook for 5-6 minutes, stirring occasionally, until the mushrooms release their moisture and become golden brown. You're looking for that deep, earthy aroma that fills your kitchen.

Don't crowd the pan—this helps the mushrooms crisp up nicely instead of steaming. If the pan gets too dry, add a splash of water, but try to keep it as dry as possible. Season lightly with ½ teaspoon ground black pepper and ½ teaspoon kosher salt while they cook. These flavors will carry through the whole dish.

In the same skillet (no need to wash it—the browned bits add flavor), reduce heat to medium-low and add the ½ cup unsalted butter. Let it melt completely, then whisk in the ½ cup all-purpose flour all at once. Cook for 1-2 minutes, stirring constantly, until the mixture turns a light golden color and smells nutty.

This is your roux foundation. If it starts to darken too quickly, lower the heat. Next, gradually whisk in the 2 cups whole milk and 1 cup chicken broth, about ½ cup at a time, making sure each addition is fully incorporated before adding more. The sauce should thicken noticeably as it simmers.

Preheat your oven to 375°F. In a large mixing bowl, combine the cooked elbow macaroni, sautéed mushrooms and onions, and the creamy sauce. Stir in the 1 cup frozen peas (thawed), 1 teaspoon dried thyme, and the drained 2 cans canned tuna in water. Mix gently but thoroughly to distribute everything evenly.

Transfer the mixture to a greased 9x13-inch baking dish. The casserole should look rich and inviting, with all those creamy swirls from the sauce. Sprinkle the top with 1 cup shredded cheddar cheese for that perfect melty finish. Bake uncovered for 25-30 minutes until bubbly and golden on top.

Remove the casserole from the oven and let it rest for 5-10 minutes before serving. This resting time lets the sauce set slightly and makes it easier to slice. The cheese should be melted and bubbly, with a golden crust on top that's just crisp enough to satisfy your craving for texture.

Serve warm with a side of crusty bread or a simple green salad. The creamy mushroom and pea sauce clings perfectly to the pasta, and each bite delivers that satisfying combination of tender tuna, earthy mushrooms, and comforting peas. Leftovers keep well in the fridge for up to 3 days—just reheat in the oven until warmed through.

Best sauces and condiments for baked tuna casserole

Classic Creamy Sauce

This velvety roux-based sauce is the heart of your casserole, and you can't skip the butter-to-flour ratio. I use ½ cup unsalted butter and ½ cup all-purpose flour cooked to a light golden color—this creates the perfect balance of richness and thickness.

For extra depth, whisk in 2 cups whole milk and 1 cup chicken broth gradually to avoid lumps. If you're watching calories, substitute half-and-half for the milk, but expect a slightly lighter texture. 🥛

Mushroom Gravy Twist

Swap the roux for a mushroom-infused sauce by sautéing 1 lb mushrooms until deeply browned, then blending them with 1 cup milk and ½ cup chicken broth until smooth. Strain through a fine-mesh sieve to remove any grit, then use this as your creamy base.

The earthy umami flavor from the mushrooms elevates the dish without needing extra seasoning. This works especially well if you love hearty, savory flavors.

Lemon-Dill Sauce

Brighten up the casserole with a zesty lemon-dill sauce by mixing ½ cup sour cream, 2 tbsp fresh lemon juice, 1 tbsp chopped fresh dill, and ½ tsp garlic powder. Stir this into the creamy sauce before baking, or drizzle it on top just before serving.

The tangy contrast cuts through the richness of the tuna and cheese, making each bite feel fresh and light. 🍋

Cheesy Garlic Sauce

For a decadent twist, blend ½ cup shredded cheddar cheese and 2 tbsp cream cheese into the creamy sauce while it's still warm. Add 1 tsp minced garlic and ¼ tsp smoked paprika for a smoky depth.

This sauce becomes even creamier as it bakes, creating a gooey, cheesy finish that pairs perfectly with the tuna. Sprinkle extra cheese on top before baking for a golden, bubbly crust.

Spicy Tomato Sauce

Add a kick by mixing ½ cup marinara sauce into the creamy base or layering it beneath the tuna mixture. For extra heat, stir in ½ tsp cayenne pepper or 1 tbsp hot sauce.

The acidity from the tomato sauce balances the richness, while the spices add complexity. This variation works especially well if you love bold, slightly tangy flavors in your casseroles. 🌶️

Herb-Infused Olive Oil

Drizzle the finished casserole with a simple herb-infused olive oil before serving. Heat 2 tbsp olive oil with 1 tbsp fresh parsley, 1 tsp fresh thyme, and a pinch of salt, then let it cool.

Pour this fragrant oil over the top just before serving for a bright, aromatic finish. This adds a fresh herbal note without altering the creamy texture of the dish.

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