Combine first 4 ingredients; set aside.
Cut a 1/4-inch-thick slice off top of each roll; set tops aside. Hollow out centers of rolls, leaving 1/2-inch-thick shells; reserve inside of rolls for another use. Place 1 lettuce leaf in bottom portion of each roll. Spoon corn mixture evenly over lettuce; top each serving with 2 tomato slices and 2 slices roast beef. Cover with roll tops.