Combine the soy sauce, vinegar, green onions, chili oil, sesame oil, garlic, ginger, and lemongrass in a bowl, and mix well. Pour the marinade into a large resealable plastic bag, and add the steaks. Squeeze the bag to remove excess air, and then seal it. Refrigerate for 24 hours, turning the bag occasionally.
Preheat a grill to high.
Remove the steaks from the marinade (discard the marinade), and blot them with paper towels to remove excess marinade. Place the steaks on the grill and cook until nicely marked on both sides, about 4 minutes on each side for medium-rare. Remove the steaks from the grill and let them rest for 10 minutes. Then thinly slice, and serve over jasmine rice if desired, garnished with chopped green onions.
Yield: 4 servings