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 on both sides. Place seasoned chicken in the prepared baking dish.
03 - Spoon 1 tablespoon of basil pesto over each chicken breast. Use the back of the spoon to spread the pesto evenly across the surface of the chicken.
04 - Place baking dish in the 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 basil, extra-virgin olive oil, balsamic vinegar, ½ teaspoon salt, and ¼ teaspoon black pepper in a medium bowl. Toss ingredients thoroughly to combine. Set aside at room temperature to allow flavors to meld.
06 - Remove chicken from oven after 15 minutes. Top each breast with one-quarter of the bruschetta mixture, spooning it evenly over the pesto layer. Sprinkle shredded mozzarella cheese generously over the top of each chicken breast.
07 - Return chicken to the oven. Bake for an additional 8–10 minutes, or until chicken is cooked through (internal temperature reaches 165°F when measured with a meat thermometer) and cheese is fully melted and lightly browned.
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.