1. Preheat grill to medium-high heat.
2. Combine first 5 ingredients in a small bowl. Rub sugar mixture evenly over steak; let stand 10 minutes. Place steak on a grill rack coated with cooking spray; cook 4 minutes on each side or until desired degree of doneness. Let stand 10 minutes; cut diagonally across grain into thin slices. Serve with lime wedges and tortillas. Garnish each serving with cilantro leaves, if desired.