Preheat half the grill to medium high. Oil grill rack with spray olive oil before placing on preheated grill. Place breasts on heated grill and brown on both sides for 10 minutes. Move all chicken pieces to side of grill without heat while keeping medium heat on the other side. Close cover and continue to cook for 10-15 minutes. Check chicken for doneness by piercing skin with tip of knife. Chicken is done when juices run clear.