Preheat your oven to 375°F (190°C). Cook the egg noodles according to the package instructions, then drain and set aside.
Prepare the casserole mixture:
In a large mixing bowl, combine the drained tuna, cooked noodles, frozen peas, cream of mushroom soup, milk, garlic powder, salt, and pepper. Stir in the shredded cheddar cheese until well combined.
Sauté the onion (optional):
If you’re using onion, sauté the chopped onion in a little butter or oil until softened (about 3-4 minutes), then add it to the casserole mixture.
Assemble the casserole:
Transfer the casserole mixture to a greased 9×13-inch baking dish. Spread it out evenly.
Prepare the topping:
In a small bowl, mix the breadcrumbs with melted butter until the breadcrumbs are evenly coated. Sprinkle the breadcrumb mixture over the top of the casserole. Add extra shredded cheddar cheese on top for a cheesy, golden finish.
Bake:
Bake in the preheated oven for about 25-30 minutes, or until the top is golden brown and the casserole is bubbly.
Serve:
Let the casserole cool for a few minutes before serving. Garnish with chopped fresh parsley if desired.
