Preheat the grill to 450-475 degrees. Add foil to the grill. Pound the chicken then toss it with olive oil, salt and black pepper. Add the chicken breasts to the grill. Grill for 10-12 minutes.
Turn the chicken over, reduce the heat to 400 and grill for another 10-12 minutes or until the internal temperature reaches 165 degrees. Add a few slices of mozzarella to the chicken. Once melted remove from the grill.
Build the Sandwich
Toast the pretzel rolls. Add one breast to each roll. Top with sliced tomatoes and lettuce. Drizzle with balsamic glaze. Top and enjoy.