In a bowl, mix olive oil, balsamic vinegar, Dijon mustard, Italian seasoning, minced garlic, salt, and pepper. Coat chicken breasts in the marinade and refrigerate for at least 1 hour.
Preheat oven to 400°F (200°C). Line a rimmed baking sheet with foil and spray with non-stick cooking spray.
Make deep cuts across the top of each breast without slicing through completely. Stuff each cut with tomato slices, mozzarella, and basil leaves.
Place stuffed chicken on prepared baking sheet; bake for 25-30 minutes until internal temperature reaches 165°F (75°C).
Allow to rest for about 5 minutes before serving. Drizzle with balsamic glaze if desired.
Nutrition
Serving Size:1 stuffed chicken breast (approx. 7 ounces)