Cook cubed chicken and red onion in a skillet until chicken is no longer pink inside. In a separate sauce pan prepare your rice, once rice is prepared add your black beans, corn, and diced tomatoes, stir together. Once the chicken is done there should be some water in the bottom of the skillet, add about half of the taco seasoning packet to the chicken and onion mixture, cook until it is thickened. Once thickened turn off heat and let sit. Take your peppers and cut them in half, and then core and clean them out. Place in a greased 13X9 cake pan empty side up. Mix together the chicken and rice mixture together. stuff each half of the green pepper until no more will fit. Do this until all of them are full. Empty the spaghetti sauce around the peppers in the cake pan. When there is about 15 min left of cooking sprinkle the top of each pepper with some cheese and pop back in until finished cooking.