In a marinating dish or large zip lock bag pour in marinating ingredients (soy sauce - mustard), stir or shake bag until sugar is dissolved. Add beef, covering all sides. Chill at least 2 hours, but may be marinated up to one day, turning occassionally.
Drain beef, discarding marinade.
Prepare grill using a solid bed of coals - about medium heat.
Grill beef, turning every 5 minutes until done to desired doneness (about 30 minues for med rare).
Transfer to platter or cutting board and let rest 5 minutes before slicing beef into thin slanting slices, cutting across grain.