01 - Preheat oven to 400°F. Lightly grease a baking dish or sheet pan with cooking spray or a small amount of olive oil.
02 - Pat chicken breasts dry with paper towels. Rub each breast with olive oil, then season evenly with salt, black 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 to cover 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 bowl. Toss well to combine all flavors and set aside.
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 dish to oven and bake for an additional 8–10 minutes, until chicken reaches an internal temperature of 165°F and cheese is melted and bubbly with light golden spots.
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.