Preheat oven to 350 degrees F.
Add the chicken, vegetables, cream of chicken soup, sour cream, garlic powder, onion powder, salt and pepper to a large mixing bowl. Stir together.
Spray a 2-quart casserole dish with nonstick cooking spray. Add the chicken mixture to the casserole dish.
Place Doritos in a zip up bag. Seal it and use a meat mallet to break the Doritos into small pieces. Top the chicken mixture with the Doritos.
Add the cheese to the top of the Doritos. Bake for 35 minutes, or until it is heated through and the cheese is melted.