Season chicken breasts with salt and pepper and cook on your 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. You can also place them on the grill with the inside facing down.
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.