Preheat the oven: Set to 400°F (200°C). Lightly oil a 9x13-inch baking dish or line with parchment for easier cleanup.
Pound the chicken (optional but helpful): If the breasts are thick, pound to an even 3/4–1-inch thickness so they cook evenly.
Season the chicken: Pat dry.
Rub with 1 tablespoon olive oil, 1 teaspoon salt, 1/2 teaspoon black pepper, and Italian seasoning. Lay in the baking dish, leaving a little space between each piece.
Make the bruschetta topping: In a bowl, combine tomatoes, basil, onion, garlic, balsamic, 1 tablespoon olive oil, 1/2 teaspoon salt, black pepper, and a pinch of red pepper flakes if using. Taste and adjust seasoning.
It should be bright and a little tangy.
Top the chicken: Spoon the bruschetta mixture evenly over each breast. If using mozzarella, add it now (either sprinkle shredded or lay a thin slice over each piece).
Bake: Cook uncovered for 22–28 minutes, depending on thickness, until the internal temperature reaches 165°F (74°C). If you want more color on the cheese, broil for 1–2 minutes at the end.
Finish: Rest for 5 minutes.
Add a little fresh basil, a light drizzle of balsamic, and a quick squeeze of lemon or a sprinkle of Parmesan for extra brightness.
Serve: Spoon pan juices over the chicken. Pair with a green salad, roasted veggies, or a side of whole grains like farro or quinoa.