01 - Preheat oven to 400°F. Lightly grease a baking dish or sheet pan with cooking spray or a thin layer of oil.
02 - Pat chicken breasts dry with paper towels. Rub with olive oil, then season evenly with salt, pepper, and Italian seasoning. Place seasoned chicken in the prepared baking dish.
03 - Spoon 1 tablespoon basil pesto over each chicken breast, spreading evenly to coat the top surface.
04 - Place baking dish in preheated oven and bake for 15 minutes to partially cook the chicken.
05 - While chicken bakes, combine diced tomatoes, red onion, minced garlic, chopped basil, extra-virgin olive oil, balsamic vinegar, salt, and pepper in a medium bowl. Toss thoroughly 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 distribute shredded mozzarella evenly over all pieces.
07 - Return dish to oven and bake for 8 to 10 minutes longer, until chicken reaches internal temperature of 165°F and cheese is melted and lightly golden.
08 - Let chicken rest for 3 to 5 minutes before serving to allow juices to redistribute. Serve with any remaining bruschetta topping spooned over the top.