In a large mixing bowl, combine the shredded chicken, cream of chicken soup, sour cream, cheddar cheese, milk, celery, onion, garlic powder, onion powder, salt, and pepper. Mix until well combined.
Transfer the chicken mixture into a greased 9×13 inch baking dish, spreading it evenly.
In a separate bowl, combine the crushed Ritz crackers and melted butter, mixing until the crackers are evenly coated.
Sprinkle the Ritz cracker mixture over the chicken casserole, covering it completely.
Bake in the preheated oven for 30-35 minutes, or until the casserole is bubbly and the cracker topping is golden brown.
Remove from the oven and let it cool for a few minutes before garnishing with fresh parsley.
