Preheat the oven to 350°F (175°C).
In a mixing bowl, combine the cooked chicken, celery, onion, garlic powder, and pepper.
Add the cream of chicken soup and stir until well combined.
In another bowl, mix the stuffing mix with chicken broth and milk.
Layer half of the stuffing mixture in a greased casserole dish.
Spread the chicken mixture over the stuffing layer.
Top with the remaining stuffing mixture.
If desired, sprinkle shredded cheese on top.
Bake uncovered for 30 minutes or until golden brown.
Let it cool for a few minutes before serving.