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 cutting all the way through.
03 - Season the outside and inside of each pocket with salt, pepper, and garlic powder.
04 - Fill each pocket with sliced mozzarella, tomato, and 3 basil leaves.
05 - Hold the filling inside by securing the openings with toothpicks.
06 - Heat olive oil in a large oven-safe skillet over medium-high heat. Sear the chicken breasts for 2 to 3 minutes per side until golden brown.
07 - Transfer the skillet to the oven or place chicken on the prepared baking tray. Bake for 18 to 22 minutes until cooked through and cheese is melted.
08 - Combine balsamic vinegar and honey in a small saucepan. Simmer over medium heat, stirring occasionally, until reduced by half and syrupy, about 8 to 10 minutes.
09 - Remove toothpicks from chicken breasts. Drizzle with balsamic reduction before serving.