Mix together the soy sauce, sugar, and garlic until the sugar dissolves. Put the meat into a container or ziplock bag and combine with marinade. Let marinate for 20 minutes or up to 5 hours, turning at least once.
Adjust rack to upper third of oven and turn on broiler. Transfer meat to a foil-lined rimmed baking sheet, reserving the marinade. Sprinkle the meat with the pepper and broil, about 5 minutes per side for medium-rare.
Transfer the meat to a cutting board. Let sit for 10 minutes before slicing thinly across the grain.
Meanwhile, place a skillet over medium-high heat and bring the marinade to a boil. Add the scallions, reduce heat to medium, and cook for 2 minutes.
Serve meat with marinade drizzled over the top and accompanied by white rice.