Preheat the oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish with non-stick spray.
Prepare the rice: Cook the Chicken Rice-A-Roni as directed on the box. Set aside.
Make the filling: In a large mixing bowl, whisk together the sour cream, cream of chicken soup, garlic powder, onion powder, salt, and pepper until smooth. Stir in the cooked chicken and prepared rice.
Assemble the casserole: Spread the chicken and rice mixture evenly into the prepared baking dish.
Make the topping: In a small bowl, combine the melted butter and crushed Ritz crackers. Stir in the shredded cheddar cheese. Sprinkle the mixture evenly over the casserole.
Bake: Bake for 25 minutes, then broil for 2–3 minutes until the top is golden and crispy.
Serve: Let cool slightly before serving. Enjoy the creamy filling with a crunchy topping in every bite.