Preheat oven to 375°F and grease a 9x13-inch baking dish.
Cook egg noodles according to package directions until just shy of al dente, then drain well.
In a large bowl, combine the cream of mushroom soup, milk, black pepper, and garlic powder until smooth.
Add the cooked noodles, tuna, peas, celery, and cheddar cheese to the soup mixture and stir until everything is well combined.
Pour the mixture into the prepared baking dish and spread evenly.
In a small bowl, toss the crushed potato chips or breadcrumbs with melted butter, then sprinkle over the top of the casserole.
Bake for 25-30 minutes until bubbly around the edges and the topping is golden brown.
Let stand for 5 minutes before serving.