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 with olive oil, then season evenly with salt, pepper, and Italian seasoning. Place in the prepared baking dish.
03 - Spoon 1 tablespoon basil pesto over each chicken breast, spreading it evenly to cover the top surface.
04 - Bake chicken for 15 minutes in the preheated oven to begin cooking through.
05 - While chicken bakes, combine diced tomatoes, red onion, garlic, fresh basil, extra-virgin olive oil, balsamic vinegar, salt, and pepper in a medium bowl. Toss well to combine and set aside to allow flavors to meld.
06 - Remove chicken from oven after 15 minutes. Top each breast with one-quarter of the bruschetta mixture, then sprinkle shredded mozzarella evenly over all pieces.
07 - Return to oven and bake for another 8-10 minutes, until chicken reaches internal temperature of 165°F and cheese is melted and lightly golden.
08 - Let chicken rest for 3-5 minutes before serving to allow juices to redistribute. Serve with any remaining bruschetta mixture spooned over the top or on the side.