Preheat oven to 425ºF. Place chicken in large resealable plastic bag or glass dish. Add 1/4 cup of the marinade; turn to coat well. Refrigerate 30 minutes or longer for extra flavor. Remove chicken from marinade. Discard any remaining marinade.
Grill chicken over medium heat 6 to 7 minutes per side or until cooked through, basting with an additional 2 tablespoons of the marinade. Cut chicken into bite-size pieces.
Toss tomatoes with remaining 2 tablespoons marinade in medium bowl. Place flatbreads on baking sheets sprayed with no stick cooking spray. Layer flatbreads evenly with half of the cheese, grilled chicken, tomatoes, remaining cheese and desired amount of basil leaves.
Bake 10 minutes or until cheese is melted and golden brown. Slice and serve immediately.