Prepare the Marinade: In a bowl or zip-top bag, combine balsamic vinegar, 1/4 cup olive oil, honey (if using), minced garlic, Italian seasoning, salt, and pepper.

Marinate the Chicken: Add the chicken breasts to the marinade, ensuring they are fully coated. Marinate in the refrigerator for at least 30 minutes, or up to 4 hours.

Prepare the Topping: In a separate bowl, gently combine the diced avocados, tomatoes, chopped fresh basil, lemon/lime juice, and a pinch of salt and pepper. Set aside. (The acid prevents browning).

Preheat and Grill: Preheat your outdoor grill or grill pan to medium-high heat. Lightly oil the grates to prevent sticking.

Cook the Chicken: Remove the chicken from the marinade and place it on the preheated grill. Cook for 5 to 7 minutes per side, or until the internal temperature reaches 165°F (74°C). Remove from heat and let rest for 5 minutes to ensure juiciness.

Assemble: Immediately place a slice or a few balls of fresh mozzarella on top of each hot chicken breast to allow the cheese to slightly melt.

Serve: Top the melted mozzarella with a generous spoonful of the fresh avocado and tomato mixture. Drizzle with balsamic glaze if desired, and serve immediately.