01 - Preheat the oven to 400°F.
02 - Pat chicken breasts dry. Using a sharp knife, cut a deep pocket into the side of each breast, being careful not to cut all the way through.
03 - Season the chicken on both sides and inside the pocket with salt, pepper, and garlic powder.
04 - Stuff each pocket with mozzarella slices, tomato slices, and 4 basil leaves. Secure with toothpicks if needed.
05 - Heat olive oil in an oven-safe skillet over medium-high heat. Sear chicken breasts for 2-3 minutes per side until golden brown.
06 - Transfer the skillet to the oven and bake for 18-20 minutes, or until chicken is cooked through to an internal temperature of 165°F.
07 - While the chicken bakes, combine balsamic vinegar and honey in a small saucepan. Simmer over medium heat until reduced by half and thickened, about 5 minutes.
08 - Remove toothpicks from chicken, drizzle with balsamic glaze, and serve immediately.