Preheat the oven to 375 degrees and lightly grease a 9x9 baking dish.
Bring a large pot of salted water to a boil. Cook the egg noodles according to package directions until just tender, then drain and return them to the pot.
Add the drained tuna, frozen peas, cream of mushroom soup, milk, 1 cup of the cheddar cheese, and a pinch of salt and pepper to the noodles. Stir everything until evenly combined.
Transfer the mixture to the prepared baking dish and spread it out into an even layer.
In a small bowl, mix the breadcrumbs with the melted butter. Sprinkle this mixture over the top of the casserole along with the remaining 1/2 cup of cheddar cheese.
Bake for 20 to 25 minutes until the cheese is melted and the topping is golden. Let it sit for a few minutes before serving.