In a small bowl, combine mayonnaise, horseradish, garlic and lemon juice. Add salt and pepper to taste.
Assemble your sandwiches:
Spread the mayonnaise mixture onto 2 slices of bread. Layer 1-2 romaine leaves on a slice of bread. Follow with 2 slices of Cooper Sharp cheese. Add 2 tomato slices, then layer 1/4 pound of the roast beef on top. Add 2 more slices of Cooper Sharp cheese. Layer about 1/4 cup sprouts on the cheese, then top with a slice of bread. Repeat to make 4 sandwiches total.