01 - Preheat oven to 400°F. Lightly grease a baking dish or sheet pan with cooking spray or oil.
02 - Pat chicken breasts dry with paper towels. Rub evenly with olive oil, salt, pepper, and Italian seasoning on all sides. Place seasoned chicken in the prepared baking dish.
03 - Spoon 1 tablespoon basil pesto over each chicken breast, using the back of the spoon to spread it evenly across the surface.
04 - Bake chicken for 15 minutes to begin the cooking process.
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 evenly with one-fourth of the bruschetta mixture, then sprinkle shredded mozzarella over the top.
07 - Return to oven and bake for 8–10 minutes longer, until chicken reaches internal temperature of 165°F and cheese is melted and lightly browned.
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.