Preheat oven to 425 degrees. Rinse chicken and if using breasts cut in half lengthwise. In a large baking dish, add chicken, garlic, salt and pepper. Mix well to coat evenly and spread in a single layer. Cover and bake for 20-25 minutes. Chicken is cooked when pale and surrounded by clear juices.
In the meanwhile, preheat large ceramic non-stick skillet on low-medium heat and swirl oil to coat. Add onion and saute for a few minutes, stirring occasionally. Add mushrooms and saute for a few more minutes, stirring occasionally. Add bell peppers and saute for 5 more minutes, stirring.
Remove chicken from the oven and turn broiler on High. Separate chicken a bit from each other and top each piece with vegetables (sprinkle around too) and top with cheese. Broil for 5 minutes or until cheese is melted. Serve hot with rice, quinoa or veggies.