01 - Set the oven temperature to 400°F (200°C) in preparation for baking.
02 - Carefully slice a horizontal pocket into each chicken breast without cutting fully through.
03 - Season the interior and exterior of each breast with salt and freshly ground black pepper.
04 - Arrange mozzarella slices, tomato slices, and 4 basil leaves inside each chicken pocket; secure openings with toothpicks if necessary.
05 - Heat olive oil in an oven-safe skillet over medium-high heat, then sear 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 until the chicken is thoroughly cooked and the cheese has melted.
07 - Combine balsamic vinegar and honey in a small saucepan; simmer over medium heat, stirring occasionally, for 5 to 8 minutes until the mixture thickens to a syrupy consistency. Remove from heat.
08 - Remove toothpicks from the chicken breasts, drizzle with balsamic glaze, and garnish with additional fresh basil leaves if desired before serving.