Add the cherry tomatoes, olives, capers, onion, garlic, parsley, and olive oil in a mixing bowl along with ½ teaspoon salt and ¼ teaspoon pepper. Toss gently to combine and allow to marinate for 30 minutes.
Preheat the grill to medium-high heat, and oil the grate. Lightly brush both sides of the chicken breasts with olive oil and season to taste with salt and pepper.
Grill the chicken for 8-10 minutes per side, until cooked through. Spoon the cherry tomato salad on top and serve immediately.