Prepare the chicken by boiling, baking, or grilling it. Once cooked, let it cool and shred into bite-sized pieces.
In a large mixing bowl, combine shredded chicken, cooked white rice, cream of chicken soup, sour cream, frozen mixed vegetables, garlic powder, onion powder, black pepper, and salt. Mix until well combined.
Grease a 9x13-inch baking dish and spread the chicken mixture evenly in the dish. Sprinkle shredded cheddar cheese on top.
Mix crushed buttery crackers with melted butter and sprinkle over the cheese layer. Bake in a preheated oven at 350°F for 30-35 minutes until bubbly and golden brown.
Let the casserole cool for 5-10 minutes before serving.