Cut the dried/frozen pollock (bukuh kodari 북어 코다리) into big, flat pieces (~2"x3"), removing the bones.
Find a baking dish or a broiler pan and place the pollock into it.
Add the garlic, onion, sesame seeds, sesame oil, sugar, jalapeno and threaded red peppers into the soy sauce and mix well. Spread the sauce on the prepared pollock and as much possible, cover the fish with the sauce.
Cover the pan with aluminum foil. Cook for about 25 min on 350 F. Can serve cool or warm.