Heat about 2 cups of water in a steamer.
Slash the fish, just like in the picture. Rub the mixture of soy sauce and citus juice all over and inside (the cavity from where the intestines have been removed) the fish. Stuff the cavity with garlic and ginger. Place fish side by side on a heatproof shallow dish. Pour the remaining soy-citrus mix over them. Place all remaining garlic and ginger on top of the fish and drizzle with sesame seed oil. Steam for 20 minutes. Serve hot.