Marinate the cleaned fish/prawns with Kashmiri chilli powder (2 tsp), Turmeric powder (1/2 tsp) and salt and keep for half an hour. Heat oil in a pan & fry the fish/prawns. Keep it aside.
Heat oil in another pan and add mustard & fenugreek seeds. When it crackles add ginger sliced, garlic sliced and green chilly chopped & curry leaves and fry till it becomes brown. Keep it aside. Add ginger garlic paste to the same pan & fry it till it becomes brown. Add chilly powder, turmeric powder and salt. Fry the masala till its done and the oil starts appearing.
Add 3-4 tbsp of water. Mix well and after a minute add fried fish/prawns, fried ginger & garlic slices & chopped green chilly & vinegar. Let it boil.
If you want more gravy, add 3-4 tbsp water. Boil it for 5 more minutes. Do a taste check and add more salt & vinegar, if required. Remove from fire & let it cool completely.
Store it in airtight container and pour the remaining fried oil over the top of the pickle.
Notes
If you're making this recipe with fish, cut it into bite size pieces. I used sunflower oil. You can use sesame oil (nallenna), corn oil etc; When you add vinegar, start with 1/2 cup and add more, after doing a taste check. Keep in mind that that it will take time for the flavor to settle in. This is a spicy recipe, please adjust the ingredient measurements to suit your taste.If you are planning to keep it for a long time, its better to refrigerate it. Also if you're living in a hot & humid climate, refrigeration is strongly recommended. Though you can start using it the day it's made, its better to keep it for 1-2 days for the flavor to settle in. Make sure that you use only boiled & cooled water.