Combine barbecue sauce, horseradish and Cajun seasoning in small bowl; mix thoroughly. Cover and refrigerate until ready to use.
Combine balsamic vinaigrette and peppers in small bowl; mix thoroughly. Cover and refrigerate until ready to use.
Combine mayonnaise, sour cream, mustard and Worcestershire sauce in large bowl. Add potatoes, green onions, bacon, chives and dill; mix thoroughly. Season with salt and pepper, as desired. Cover and refrigerate until ready to use.
Brush beef Flank Steak with barbecue sauce. Place steak on grid over medium, ash-covered coals. Grill, covered, 11 to 16 minutes (over medium heat on preheated gas grill, covered, 16 to 21 minutes) for medium rare (145°F) to medium (160°F) doneness, turning occasionally and basting with remaining barbecue sauce during last 5 to 10 minutes. Remove steak from grill; thinly slice steak diagonally across the grain; keep warm.
Divide lettuce between four plates. Top with potato salad and steak. Drizzle with prepared balsamic dressing and peppers. Season with salt and pepper, as desired. Garnish with onions, as desired.
Nutrition information per serving: 584 Calories; 278.1 kcal Calories from fat; 30.9 g Total Fat; 7.7 g Saturated Fat; 0.2 g Trans Fat; 6.7 g Polyunsaturated Fat; 5.6 g Monounsaturated Fat; 87 mg Cholesterol; 896 mg Sodium; 38.7 g Total Carbohydrate; 3.5 g Dietary Fiber; 28.9 g Protein; 3.6 mg Iron; 1109 mg Potassium; 8.5 mg Niacin; 0.8 mg Vitamin B6; 1.5 mcg Vitamin B12; 5 mg Zinc; 28.6 mcg Selenium; 126.1 mg Choline;