Marinate the fish pieces with chilli powder, salt and turmeric powder for at least 30 minutes.
If you are using big pieces, you can lightly fry the fish and then break into smaller bits.
Heat oil for deep frying.
Tip in the fish and fry till brown in colour.
Drain and keep aside.
Mix the chilli powder, turmeric powder and fenugreek powder with a little water to form a paste. Keep aside.
Take another pan.
Pour some oil (in which the fish was fried) into the pan.
Add the mustard seeds.
When they start to crackle, add the curry leaves.
Tip in the ginger-garlic pastes and saute till the raw smell goes.
Add the chilli paste and fry till oil separates.
Add the fried fish pieces and mix well, carefully.
Add the vinegar, followed by boiled and cooled water.
Check and adjust seasoning.
When the mixture comes to a rolling boil, switch off heat.
Allow to cool completely before transferring to an air tight jar.
You can store in a refrigerator for longer duration.