Lay the steaks on a tray.
In a small bowl, combine the fish sauce, lime juice, soy sauce, pepper, sugar and sesame oil. Rub the steaks with this mixture, rubbing it evenly over each side. Allow to marinate at room temperature for 30 minutes.
Preheat the oven grill to high or make a charcoal fire in the barbecue. When the oven grill is very hot or the charcoal is ash white, grill