Pre-heat a grill or grill pan to medium high heat.
If chicken breasts are too thick, place between two pieces of plastic wrap or parchment and flatten with the smooth side of a meat mallet to 1 ½ inch. Place meat in a bowl or zip top bag.
Blend the oil, vinegar, garlic and salt and pepper and pour over the chicken. Toss to coat the chicken and let marinate for 15 minutes before grilling.
When grill is hot and chicken marinated, cook breasts for about 5-7 minutes per side and brush often with extra balsamic vinegar to set in the flavor. Internal temperature of chicken should read about 155°- 160°. Move chicken to cool side of the grill and tent with foil or remove chicken to a plate and tent with foil for 5-6 minutes. Prepare Caprese salad (below)