01 - Preheat the oven to 400°F.
02 - Use a sharp knife to cut a horizontal pocket in each chicken breast, ensuring not to slice all the way through.
03 - Season the interior and exterior of each chicken breast with salt and freshly ground black pepper.
04 - Layer slices of mozzarella, tomato, and 4 basil leaves inside each chicken pocket. Secure with toothpicks if necessary.
05 - Heat olive oil in an oven-proof skillet over medium-high heat and sear stuffed chicken breasts for 2 to 3 minutes per side until golden brown.
06 - Transfer the skillet to the preheated oven and bake for 20 to 25 minutes, or until the chicken is fully cooked and the cheese has melted.
07 - In a small saucepan, combine balsamic vinegar and honey. Simmer over medium heat for 5 to 8 minutes, stirring occasionally, until thickened to a syrupy consistency. Remove from heat.
08 - Remove toothpicks from chicken breasts, drizzle with the balsamic glaze, and garnish with extra basil leaves if desired.