Preheat the oven to 375 degrees and lightly grease a 9-by-13-inch baking dish.
Bring a large pot of salted water to a boil and cook the egg noodles until just tender. Drain and set aside.
In a large bowl, stir together the cream of mushroom soup, milk, salt, and pepper until smooth.
Add the drained tuna, frozen peas, and cooked noodles to the bowl. Mix gently until everything is coated.
Spread the mixture evenly into the prepared baking dish.
In a small bowl, toss the breadcrumbs with the melted butter until evenly moistened. Sprinkle the mixture over the top of the casserole.
Bake for 20 to 25 minutes until the topping is golden and the edges are bubbling. Let it rest for a few minutes before serving.