Preheat the oven to 400°F and prepare a casserole dish.
In a large bowl, combine the cooked egg noodles, cream of mushroom soup, drained tuna, frozen peas, and milk. Mix until well combined.
Spread the mixture evenly into the prepared casserole dish.
Bake for about 30 minutes, or until the casserole is heated through.
In a small bowl, mix the breadcrumbs with the melted butter.
Sprinkle the breadcrumb mixture evenly over the casserole.
Return to the oven and bake for another 5 minutes, or until the topping is golden.
Let the casserole sit briefly before serving.