01 - Preheat oven to 400°F. Lightly grease a baking dish or rimmed sheet pan with cooking spray or a small amount of oil.
02 - Pat chicken breasts dry with paper towels. Rub each breast evenly with olive oil, then sprinkle with salt, black pepper, and Italian seasoning on all sides. Arrange seasoned chicken in the prepared baking dish.
03 - Spoon 1 tablespoon of basil pesto over each chicken breast. Spread evenly across the surface using the back of the spoon to coat the top.
04 - Place baking dish in preheated oven. Bake for 15 minutes to partially cook the chicken and set the pesto layer.
05 - While chicken bakes, combine diced tomatoes, red onion, minced garlic, chopped fresh basil, extra-virgin olive oil, balsamic vinegar, ½ teaspoon salt, and ¼ teaspoon black pepper in a medium mixing bowl. Toss thoroughly to combine all flavors. Set aside at room temperature.
06 - Remove chicken from oven after 15 minutes. Top each breast with one-quarter of the bruschetta mixture, distributing evenly. Sprinkle shredded mozzarella cheese over the topped chicken breasts.
07 - Return dish to oven and bake for an additional 8-10 minutes. Cook until chicken reaches internal temperature of 165°F and cheese is fully melted and lightly golden.
08 - Remove from oven and let chicken rest for 3-5 minutes before serving. This allows juices to redistribute. Serve with any remaining bruschetta mixture spooned over the top or on the side.