Preheat oven to 375°F (190°C).
Boil potatoes until tender, then drain and set aside.
In a mixing bowl, combine the chicken, cream of chicken soup, milk, garlic powder, salt, and pepper.
Layer the sliced potatoes at the bottom of a greased casserole dish.
Pour the chicken mixture over the potatoes.
Top with shredded cheese and drizzle melted butter.
Bake for 25-30 minutes, or until the cheese is bubbly and golden.
Let it cool for 5 minutes before serving.
