Courtesy of Kikkoman.
Whisk together the soy sauce, brown sugar, sesame oil, garlic and ginger powder in a medium bowl. Place the steak in a gallon size resealable zip close plastic bag, pour the marinade over the steak, seal the bag and turn the steak over to coat. Marinate in the refrigerator for at least 2 hours.
When ready to cook, remove the steak from the marinade, discarding the leftover liquid. Grill or broil to desired doneness.