In a small bowl, whisk together balsamic vinegar, garlic powder, honey, oil, and Italian seasoning and season with salt and pepper. Pour over chicken breasts and marinate 20 minutes.
Heat grill to medium high. Grill chicken until internal temperature reaches 170ºF on an instant-read thermometer.
Top chicken with mozzarella, avocado, and tomato and cover grill to melt, 2 minutes.
Garnish with basil and drizzle with balsamic glaze.
Recipe by Cooking TV Recipes at https://cookingtv-channel.com/california-grilled-chicken/