Combine all marinade ingredients (everything from the soy sauce to the onion) in a small blender or food processor and process until smooth. Pour over ribs in a shallow baking dish and stir to coat evenly. Cover and marinate at room temperature for 30 minutes or in the fridge for up to 48 hours.
Preheat grill over high heat for about 10 minutes. Grill ribs over direct heat for about 3 minutes on the first side (or until ribs release easily and are well marked), with lid closed, then flip and cook 1-2 minutes on the other side. Transfer to a serving plate, tent with foil and let rest for 5 minutes. Sprinkle with sesame seeds and/or chives/green onions, if desired.
(Alternatively, ribs can be cooked directly under a preheated broiler or on a lightly-oiled stovetop grill pan, preheated for at least 5 minutes over high heat.)