Preheat oven to 350º F. Spray a 9x13-inch baking dish with cooking spray.
Prepare Rice-A-Roni according to package directions.
In a large bowl, combine soup, sour cream, garlic, onion powder, chicken, mixed vegetables, and cheese. Add cooked rice and stir until well combined.
Spread rice mixture into prepared pan.
In a small bowl, combine melted butter and crushed crackers. Sprinkle cracker crumbs over the casserole.
Bake uncovered for 30 minutes.
