Mix the sour cream, mayonnaise, horseradish, mustard, lemon juice, 1/2 teaspoon of salt in a bowl. Season the beef with pepper and the remaining salt. Heat the oil in nonstick skillet. Add the steaks, cook for 1 to 2 minutes per side, until cooked through. Place the lettuce leaf on the bottom half of each roll, add the steak, top with a cucumber, peppers and horseradish sauce. Place the top on each roll.