Preheat oven to 350°F (175°C).
In a large mixing bowl, combine the shredded chicken, sour cream, cream of chicken soup, milk, garlic powder, onion powder, salt, and pepper.
Spread the chicken mixture evenly in a greased 9x13-inch baking dish.
In a separate bowl, combine the crushed Ritz crackers and melted butter, stirring until the crackers are well-coated.
Sprinkle the buttery cracker mixture evenly over the chicken layer in the baking dish.
Finally, bake in the preheated oven for 25-30 minutes, or until the casserole is bubbly and the topping is golden brown.
Let the casserole cool for 5-10 minutes before serving.