Preheat the oven to 350°F (175°C).
Cook the elbow macaroni according to package instructions until al dente. Drain and set aside.
In a large skillet over medium heat, melt the butter. Add the chopped onion and sliced mushrooms and sauté for 5 minutes until softened.
Sprinkle the flour over the butter, onion, and mushrooms, stirring constantly to form a roux. Cook for 1-2 minutes without browning.
Gradually whisk in the milk, continuing to whisk until the sauce thickens and is smooth, about 5 minutes.
Remove the sauce from heat and stir in the shredded cheddar cheese, grated Parmesan cheese, garlic powder, onion powder, black pepper, and salt until the cheese is melted and the sauce is creamy.
In a large mixing bowl, combine the cooked macaroni, tuna, thawed peas, and cheese sauce. Stir gently to combine.
Transfer the mixture to a greased 9×13 inch baking dish and spread evenly.
In a small bowl, mix the panko breadcrumbs with olive oil and chopped parsley until coated.
Sprinkle the breadcrumb mixture evenly over the casserole.
Bake uncovered for 25-30 minutes, or until the top is golden brown and the casserole is bubbly.
Remove from oven and let rest for 5 minutes before serving.