Cut the fish into small cube like pieces of approx 3cmX3cm.
Marinate with 1/2 tsp of turmeric, 2 tsp of chilly powder and salt for atleast an hour.
Lightly fry the marinated fish in oil.
:- Take care not to deep fry, as the fish will become hard.
Keep aside for draining.
Heat oil in a kadai or a pan.
Splutter mustard seeds and light fry fenugreek seeds.
Add onions and fry, till they become golden brown.
Add the remaining chilly powder and turmeric powder.
Add the ginger-garlic paste and saute.
Add salt.
Saute, till the mix turns dark.
Add the fried fish to this along with lots of oil.
Cook for 10 - 15 minutes.
Allow it to cool.
As soon as it cools, transfer it to an air tight bottle.
Add vinegar and turn the bottle upside down for the vinegar to reach everywhere.
Keep aside for a day or 2.