Combine all batter ingredients in a medium sized bowl. Mix them well. Transfer the mixture into a jug that has a spout for easy pouring.
Preheat a bungeoppang pan over medium low heat. Quickly brush the pan with some melted butter or cooking oil.
Pour the batter mixture onto the bungeoppang pan. Only cover about 50 % of the pan. Add your choice of filling then add more batter mixture on top to cover the fish mould. Close the pan and turn it over quickly.
Cook both sides of the pan until the fish pastry turns golden brown (about 2 mins each side). Remove the fish pastry from the pan and cool down on the rack briefly. Serve.