Preheat the oven to 425°F (220°C). Lightly oil a 9x13-inch baking dish.
Place the chicken breasts in the prepared baking dish in a single layer and set aside.
In a small bowl, whisk together 2 tablespoons olive oil, 2 tablespoons balsamic vinegar, 1 tablespoon Italian seasoning, 2 teaspoons minced garlic, 1/2 teaspoon salt, and 1/4 teaspoon black pepper.
Pour the marinade over the chicken and turn each breast a few times in the dish so both sides are coated.
Bake the chicken in the preheated oven for 30–40 minutes, or until the internal temperature reaches 165°F (74°C) at the thickest part.
While the chicken bakes, make the bruschetta: combine the diced Roma tomatoes, 1/3 cup chopped basil, 1 tablespoon extra-virgin olive oil, 1 tablespoon balsamic vinegar, 1 teaspoon garlic powder, 1/4 teaspoon salt, and 1/4 teaspoon black pepper in a medium bowl; stir to combine.
When the chicken is fully cooked, place a slice of mozzarella on each breast and spoon the bruschetta mixture on top.
Return the pan to the oven for 3–5 minutes to melt the cheese, or broil for 1–2 minutes while watching closely.
Let the chicken rest for at least 5 minutes before serving to retain juices, then serve.