Preheat oven to 350°F (175°C). Grease a 9x13-inch baking dish.
In a large bowl, mix together cream of chicken soup, sour cream, milk, salt, and pepper.
Add cooked noodles, chicken, peas, and carrots to the bowl and stir until everything is coated.
Transfer mixture to the prepared baking dish and spread evenly.
Sprinkle shredded cheddar cheese over the top.
Combine melted butter with breadcrumbs, then sprinkle over the casserole.
Bake uncovered for 30–35 minutes, until bubbly and golden brown on top.
Let cool slightly before serving.