In a small bowl, whisk together ¼ cup olive oil with lemon juice, salt, pepper and Italian seasoning. Place chicken breasts in a large plastic bag or shallow baking dish and pour marinade over top. Marinate for at least 30 minutes or up to 1 hour.
Preheat grill to medium high heat.
Combine tomatoes, garlic, onion, balsamic vinegar, basil and remaining tablespoon of olive oil. Season to taste with salt and pepper. Set aside.
Remove chicken from marinade, shaking off excess. Grill 5-7 minutes per side or until cooked through. Place one slice of cheese on each chicken breast. Close grill to allow cheese to melt (about another minute).
Remove chicken from grill and divide bruschetta topping evenly among chicken breasts. Serve immediately.