01 - Preheat oven to 400°F.
02 - Pat chicken breasts dry. Use a sharp knife to cut a deep lengthwise pocket into each breast without cutting through.
03 - Season both sides and interior pockets of the chicken with kosher salt, black pepper, and garlic powder.
04 - Fill each pocket with mozzarella slices, tomato slices, and 4 basil leaves. Secure with toothpicks if necessary.
05 - Heat olive oil in an oven-safe skillet over medium-high heat. Sear stuffed chicken breasts for 2 to 3 minutes per side until golden brown.
06 - Transfer skillet to oven. Bake for 18 to 22 minutes until the chicken reaches an internal temperature of 165°F.
07 - While chicken bakes, combine balsamic vinegar and honey in a small saucepan. Bring to a boil, then reduce heat and simmer for 5 to 7 minutes, stirring occasionally, until thickened.
08 - Remove chicken from oven and let rest for 5 minutes. Remove toothpicks, drizzle with balsamic glaze, and garnish with basil and olive oil if desired. Serve immediately.