For the sauce: Heat the oils over medium-high heat in a heavy-bottomed, medium-sized saucepan. Add the green onions and garlic and cook until soft, about 5 minutes. Whisk in gochujang, brown sugar, soy sauce, vinegar and water over low heat until smooth and slightly thickened, about 30 minutes. Set aside until needed.
For the marinade: Combine soy sauce, mirin, sugar, vinegar and garlic in a medium-sized bowl; whisk to blend well. Pour into large, heavy-duty ziplock bag. Add ribs; seal bag. Turn bag over several times to coat ribs evenly. Refrigerate overnight, turning bag occasionally.
For the ribs: Prepare barbecue grill to medium-high heat. Remove ribs from marinade and wipe clean. Working in batches, grill ribs until browned and cooked to medium rare, about 3 minutes each side. Apply the barbecue sauce over ribs just before serving. Mound ribs on platter or serve individually.