In a medium bowl, combine the green onions, soy sauce, brown sugar, garlic, rice wine vinegar, sesame oil, red pepper flakes and lime zest and juice and whisk together. Place the steak in a resealable plastic bag. Add half of the marinade. Seal the bag and chill in the fridge for at least 4 hours or up to 24 hours. Cover and chill the remaining marinade mixture.

Preheat the grill to medium-high heat (350 to 400 degrees F). Spray the grill rack with nonstick, nonflammable cooking spray.

Remove the steak from the marinade, discarding the marinade. Grill the steak until a thermometer registers 155 degrees F, or to desired degree of doneness, 8 to 10 minutes per side. Remove from the heat and let stand for 10 minutes before slicing across the grain.

Serve the steak in lettuce leaves with desired toppings and the remaining marinade.