Make the bruschetta topping: Dice the Roma tomatoes into small chunks. Finely mince the red onion. Chop the fresh basil. In a large bowl, combine the tomatoes, red onion, basil, 1 tablespoon olive oil, shaved parmesan, and salt and pepper to taste. Toss gently and set aside at room temperature while you cook the chicken.
Pound the chicken breasts to an even 1/2-inch (1.25cm) thickness using a meat mallet or rolling pin between two sheets of plastic wrap. Season both sides with half the Italian seasoning, minced garlic, salt, and pepper.
Heat the remaining 1 tablespoon olive oil in a large skillet over medium-high heat. Add the chicken breasts (work in batches if needed to avoid crowding) and sear for 5–6 minutes per side until golden and cooked through.
Check the internal temperature with an instant-read thermometer — it should reach 165°F / 74°C.
Transfer the cooked chicken breasts to plates and spoon the bruschetta topping generously over each breast. Serve immediately.