How to Make It
Make the marinade: In a small bowl, combine the soy sauce, garlic, ginger, chili sauce, and sesame oil. Reserve ¼ cup for serving. Place the rest of the marinade in a large resealable plastic bag with the flanken and refrigerate for at least 1 hour and up to 24 hours.
Heat grill to medium-high. Remove the ribs from the marinade (discard the marinade) and grill for 5 to 6 minutes per side for medium-rare. Serve with the reserved marinade.