1Heat gas or charcoal grill. Sprinkle steaks with salt and 1/4 teaspoon of the pepper. Carefully brush oil on grill rack. Place steaks on grill over medium-high heat. Cover grill; cook 10 minutes, turning once, or until of desired doneness. Remove steaks from grill. Cover loosely; let stand 10 minutes.
2Meanwhile, in large bowl, toss lettuce, tomatoes and cucumber; divide salad among 4 serving plates. In small bowl, stir sour cream, onion, chives, horseradish, lemon juice and remaining 1/4 teaspoon pepper with wire whisk until well blended.
3Cut steaks across grain into thin slices; arrange over salads. Drizzle with dressing.