01 - Preheat oven to 400°F. Lightly grease a baking dish or sheet pan with cooking spray or a small amount of oil.
02 - Pat chicken breasts dry with paper towels. Rub each breast evenly with olive oil, then sprinkle both sides with salt, pepper, and Italian seasoning. Place seasoned chicken in the prepared baking dish.
03 - Spoon 1 tablespoon of basil pesto over each chicken breast, spreading it evenly across the top surface.
04 - Place baking dish in the preheated oven and bake for 15 minutes to partially cook the chicken.
05 - While chicken bakes, combine diced tomatoes, red onion, minced garlic, chopped fresh basil, extra-virgin olive oil, balsamic vinegar, salt, and pepper in a medium mixing bowl. Toss thoroughly to combine all ingredients and set aside to allow flavors to meld.
06 - Remove chicken from the oven after 15 minutes. Top each breast evenly with one-quarter of the bruschetta mixture, then sprinkle shredded mozzarella cheese over the top.
07 - Return the dish to the oven and bake for an additional 8 to 10 minutes, until chicken reaches an internal temperature of 165°F and the cheese is melted and lightly golden.
08 - Let the chicken rest for 3 to 5 minutes before serving to allow juices to redistribute. Serve accompanied by any remaining bruschetta topping.