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