Cook the chicken breasts on the grill 3-4 minutes on each side. Carefully slice each breast into two thinner breasts, making 4; set aside.
Combine caesar dressing and parmesan cheese in a bowl; add chicken breasts and coat with the dressing.
Broil bread slices for 1 minute with the inside facing up. Place a chicken breast on four of the bread slices. Top with romaine lettuce and two tomato slices. Spread any extra dressing on top bread slice, if desired. Cover sandwich with top bread slice and enjoy!