In a separate bowl, for the chicken topping, combine the tomatoes, garlic, basil, pinch of salt and balsamic vinegar. Toss until the balsamic mixture covers all of the ingredients. Set aside.
Spray the grill with cooking spray and put your chicken on to cook.
Brush the top of the chicken breast with the balsamic mixture.
Cook for about 5 minutes and flip the chicken.
Brush the other side with the balsamic mixture and cook for an additional 5-8 minutes or until juices run clear.
During the last 4 minutes place a slice of mozzarella over each chicken breast.