Assemble the Sandwich: Lay out slices of the whole grain bread. Spread horseradish sauce on one side of wach slice. Layer with lettuce, tomato, cucumber, onion, banana peppers, roast beef, and cheese. Top each sandwich with the remaining slices of whole grain bread.
Mix together the sparkling water and lemon slices.
Slice each sandwich in half if desired; serve with chips, pickle and lemon sparkling water.