Preheat your oven to 350°F.
In a large mixing bowl, combine the cooked chicken, cream of chicken soup, sour cream, shredded cheddar cheese, frozen mixed vegetables, garlic powder, onion powder, and black pepper. Mix until well combined.
In another bowl, combine the stuffing mix with the chicken broth and melted butter. Stir until the stuffing is evenly moistened.
Spread the chicken mixture evenly in a greased 9x13-inch baking dish. Top with the stuffing mixture, spreading it out evenly over the chicken.
Cover the dish with aluminum foil and bake in the preheated oven for 25 minutes. Remove the foil and bake for an additional 15-20 minutes, or until the stuffing is golden brown and the casserole is heated through.
Let the casserole cool for about 5 minutes before serving.