Prepare the chicken breasts: Place each breast on a cutting board and make a pocket by slicing horizontally into the side, taking care not to cut all the way through.
In a bowl, mix the halved cherry tomatoes, mozzarella balls, chopped basil, balsamic glaze, minced garlic, salt, and pepper.
Spoon the tomato and mozzarella mixture into each chicken breast pocket, filling generously.
Secure the openings of the chicken breasts with toothpicks or tie them with kitchen twine to keep the filling from spilling out during cooking.
In a large oven-safe skillet, heat olive oil over medium-high heat. Add the stuffed chicken breasts and sear for about 3-4 minutes on each side, until golden brown.
Sprinkle the Italian seasoning over the chicken breasts, then transfer the skillet to the preheated oven. Bake for 20-25 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (74°C).
Remove the chicken from the oven, allow it to rest for 5 minutes before slicing, then remove the toothpicks or twine.
Drizzle any remaining juices from the skillet over the sliced chicken, and garnish with additional basil if desired.
Notes
Let the chicken rest before slicing for juicier meat.