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 each breast with olive oil, then coat evenly with salt, black pepper, and Italian seasoning. Place seasoned chicken in the prepared baking dish.
03 - Spoon 1 tablespoon basil pesto over each chicken breast, spreading it evenly across the surface.
04 - Bake chicken in preheated oven for 15 minutes to partially cook through.
05 - While chicken bakes, combine diced tomatoes, red onion, minced garlic, chopped basil, extra-virgin olive oil, balsamic vinegar, ½ teaspoon salt, and ¼ teaspoon black pepper in a medium bowl. Toss thoroughly to combine and set aside.
06 - Remove chicken from oven after 15 minutes. Top each breast evenly with one-quarter 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 bubbly.
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.