Cook the Pasta:
Preheat your oven to 350°F (175°C). Cook the pasta according to package instructions until al dente. Drain and set aside.
Prepare the Sauce:
In a large skillet, combine the cream of mushroom soup, sour cream, milk, garlic powder, onion powder, salt, and pepper. Stir until smooth and heated through over medium heat.
Combine the Ingredients:
In a large mixing bowl, combine the cooked pasta, flaked tuna, frozen peas (if using), and half of the shredded cheddar cheese. Pour the creamy sauce over the mixture and stir until everything is well coated.
Assemble the Casserole:
Transfer the tuna pasta mixture into a greased 9x13-inch baking dish. Spread it evenly and top with the remaining shredded cheddar cheese.
Add the Topping:
In a small bowl, mix the melted butter with the breadcrumbs. Sprinkle the breadcrumb mixture evenly over the top of the casserole.
Bake:
Bake in the preheated oven for 25-30 minutes, or until the cheese is melted, bubbly, and the breadcrumbs are golden brown.
Serve:
Let the casserole cool for a few minutes before serving. Serve warm, and enjoy this hearty, creamy meal.