Preheat oven to 375°F. Butter or spray with nonstick spray a 9"x13" baking dish.
Cook egg noodles according to the package instructions until al dente. Drain and set aside.
In a large bowl, stir together cream of mushroom soup and milk until smooth. Add the thawed peas, flaked tuna, 1 ½ cups of the shredded cheddar cheese, garlic powder, onion powder, and seasoning salt or salt and pepper.
Add the cooked noodles to the sauce mixture and gently stir until the noodles are evenly coated and the cheese is melted.
Transfer the mixture to the prepared baking dish. Sprinkle the remaining cheese evenly over the top.
In a small bowl, mix breadcrumbs with butter until the breadcrumbs are evenly coated. Sprinkle evenly over the cheese layer.
Bake 25-30 minutes, or until the top is golden brown and the casserole is bubbly. If desired, sprinkle chopped fresh parsley over the top before serving.
