01 - Preheat the oven to 400°F.
02 - Using a sharp knife, carefully cut a horizontal pocket into each chicken breast without slicing all the way through.
03 - Season the chicken breasts inside and out with salt and freshly ground black pepper.
04 - Stuff 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 and sear the stuffed chicken breasts for 2 to 3 minutes per side until golden brown.
06 - Transfer the skillet to the oven and bake for 20 to 25 minutes, until the chicken is fully cooked and the cheese has melted.
07 - While the chicken bakes, combine balsamic vinegar and honey in a small saucepan. Simmer over medium heat for 5 to 8 minutes, stirring occasionally, until thickened and syrupy. Remove from heat.
08 - Remove toothpicks from the chicken. Drizzle the balsamic glaze over the stuffed breasts and garnish with extra basil leaves if desired.