01 - Set oven to 400°F and line a baking tray with parchment paper.
02 - Using a sharp knife, carefully cut a pocket into each chicken breast without slicing entirely through.
03 - Season both inside and outside of the chicken breasts with salt, black pepper, and garlic powder.
04 - Fill each pocket with slices of mozzarella, tomato, and 3 basil leaves.
05 - Close openings with toothpicks to keep the filling in place.
06 - Heat olive oil in an oven-safe skillet over medium-high heat. Sear chicken breasts for 2 to 3 minutes on each side until golden brown.
07 - Transfer skillet to the oven or place chicken on the prepared baking tray. Bake 18 to 22 minutes until cooked through and cheese is melted.
08 - Combine balsamic vinegar and honey in a small saucepan over medium heat. Simmer and reduce by half until syrupy, approximately 8 to 10 minutes.
09 - Remove toothpicks from chicken and drizzle with balsamic reduction before serving.