In small bowl, combine sauce ingredients.
Spread one side of each bread slice with 2 teaspoons sauce. Top with equal amounts of cucumber, onion and deli roast beef. Spoon remaining sauce evenly over beef; sprinkle with chives.
Nutrition information per serving: 246 Calories; 54 kcal Calories from fat; 6 g Total Fat; 69 mg Cholesterol; 253 mg Sodium; 19 g Total Carbohydrate; 27 g Protein; 3.4 mg Iron;