01 - Preheat oven to 350°F. Lightly grease a 9×13-inch baking dish. Bring a large pot of salted water to a boil, cook wide egg noodles until just al dente according to package instructions; drain and set aside.
02 - In a large saucepan over medium heat, melt the unsalted butter. Whisk in flour and cook for 1 to 2 minutes until light golden. Gradually add milk, whisking continuously until smooth. Stir in cream of mushroom soup and cook for 3 to 4 minutes until the sauce has thickened.
03 - Remove the saucepan from heat. Stir in shredded sharp cheddar cheese, garlic powder, onion powder, salt, and black pepper. Mix until cheddar is fully melted and well blended.
04 - In the greased baking dish, combine cooked egg noodles, drained tuna, frozen peas, and sliced mushrooms. Gently toss to distribute evenly. Pour the creamy sauce over the mixture and fold together until thoroughly coated.
05 - In a small mixing bowl, blend panko breadcrumbs, melted butter, grated Parmesan cheese, and chopped parsley. Sprinkle the topping evenly over the casserole surface.
06 - Cover the dish with aluminum foil and bake for 20 minutes. Uncover and continue baking for 10 minutes or until the topping is golden brown and the casserole is bubbling. Allow to rest for 5 minutes before serving.