Preheat oven to 400 degrees F. Spray nonstick 9x13 pan to grease. Chicken breasts should be no more than 1" thick, pound chicken down if needed.
Combine Chex, 1/4 cup Parmesan cheese, Italian seasoning, garlic powder, cayenne, and paprika in food processor. Pulse until you get a fine, even consistency from your coating mixture. Pour into wide, shallow bowl.
Beat egg with salt and pepper to taste in wide, shallow bowl.
Dip chicken in egg mixture and dredge in coating. Place in pan, and bake for 20 minutes or until coating is set and golden.
Remove pan with chicken from the oven, and pour sauce over the top of chicken. Top with remaining cheese, cover with foil, and bake for 15-20 minutes more until chicken is done and sauce is heated through.
Serve with hot cooked GF pasta (Sam Mills is my favorite) or polenta and a green salad.
***Allergen modifications: Try using plain yogurt to coat chicken instead of egg if you are allergic to eggs. Leave cheese out of coating mixture and topping if you are dairy free.