Fried the katal thin belly pieces both sides just to remove the raw smell here I took 5 katal piece.. Don't over fry them.. I took 2 table spoon mustard powder and soak it for half an hour with half teaspoon salt...

Now mix the fish pieces with the mustard powder paste along with 2 teaspoon coconut paste, 2 teaspoon poppy seed paste, half teaspoon cumin powder, turmeric powder and cumin powder, add one sliced medium onion, 2 teaspoon paste made of 3 green chilli, 2 garlic cloves, 2 table spoon mustard oil.. Now transfer the marinated fish pieces into a tiffin box, add little water and cover it tightly..

Now take a kadai add 2 cups water onto it and let it to boil, now keep the tiffin box in the kadai and medium the flame.. After 40 minutes open the lid and add 3 slited green chilli, 1 table spoon mustard oil and close the lid and keep it aside.. Katla vape is ready to serve.