HEAT oven to 400ºF.
MAKE cut in one long side of each chicken breast, being careful to not cut through to opposite side. Fill each pocket with 2 basil leaves and 1 each cheese slice and sun-dried tomato.
PLACE chicken on one side of rimmed baking sheet sprayed with cooking spray; add tomatoes to other side of baking sheet. Brush chicken evenly with 1 Tbsp. dressing.
BAKE 30 min. or until chicken is done (165ºF).
CUT remaining basil leaves into thin slices. Top tomatoes with basil and remaining dressing; toss lightly. Serve chicken topped with tomato mixture.