If the chicken breasts are very large, cut them in half lengthwise. Pat the chicken breasts dry with paper towels. Place the breasts between sheets of plastic wrap and pound them with a kitchen mallet until they are an even thickness. Season the chicken with garlic, rosemary, salt, and pepper, and rub with the oil. Let marinate for 30 minutes.

Heat a grill pan or skillet well, then sear and cook the chicken breasts. While the chicken is cooking, fry the plantain slices. Serve with the caper dressing, fried plantains, and mango slices.