1. Stir together garlic, ginger, 3 tbsp lime juice, pepper flakes, 2 tsp sugar and salt. Pour over steak in an ovenproof dish, coating both sides. Marinate in refrigerator 20 min.
2. Meanwhile, bring a large pot of salted water to a boil. Add green beans and cook until just tender, 2 to 3 min; immediately submerge in a bowl of ice water to cool. Drain and set aside.
3. For the dressing, whisk together 5 tbsp lime juice, soy sauce, 2 tsp sugar, fish sauce and oil. Transfer to a serving bowl.
4. Heat broiler to high. Broil steak 6 inches from heat, turning once, 5 min per side. Remove from oven and let rest 5 min.
5. Arrange lettuce leaves on a large platter with green beans, pineapple, tomatoes, cucumber and scallions. Slice steak across the grain and place on platter. Serve with dressing on the side. 8 to 10 servings