Horseradish spices up low-fat mayonnaise and sour cream so that you won't even notice that fat is missing.
Combine first 3 ingredients in a small bowl; stir well.
Spread sour cream mixture evenly over cut sides of rolls. Divide roast beef evenly over 4 bread halves. Top roast beef evenly with lettuce and tomato. Place remaining bread halves, sour cream mixture down, over tomato.
Oxmoor House Healthy Eating Collection