1. Place steak in freezer 15 minutes. Remove from freezer; cut across the grain into 1/8-inch-thick slices. Combine sugar and next 6 ingredients (through oil) in a large zip-top plastic bag; seal bag, and shake. Remove 3 tablespoons marinade, and set aside. Add steak to marinade in bag; seal and shake. Marinate in refrigerator for 1 hour. Remove steak from bag; discard marinade. Heat a large skillet over medium-high heat. Coat pan with cooking spray. Add steak to pan, and cook for 1 minute on each side.
2. Divide steak evenly among lettuce leaves. Top each leaf with 4 teaspoons cucumber, 4 teaspoons onion, 4 teaspoons carrot, and 2 teaspoons cilantro; drizzle with reserved 3 tablespoons marinade.