Coat flank steak with 1 teaspoon oil. Coat red peppers and green onions with remaining 2 teaspoons oil. Season, if desired, with ground black pepper. Grill steak and vegetables, turning once, until steak is desired doneness and vegetables until tender, about 12 minutes. Let steak stand 10 minutes; thinly slice. Chop green onions and slice peppers. Toss vegetables with 2 tablespoons Wish-Bone® Chipotle Ranch Dressing.
Arrange lettuce on serving platter. Top with mango, steak, peppers and onions. Just before serving, drizzle with remaining Dressing.