In a pan, heat oil and add the prawns and cook until soft and tender. Remove from the pan and set aside.
In the same hot oil, add the mustard seeds, dry red chillies and the curry leaves and let them splutter and switch off the flame.
Add the red chilli powder when the above seasoning becomes warm. Otherwise, the red chilli powder will get burned when added to hot seasoning.
Now switch on the flame in very low and add the prawns, salt and vinegar and mix thoroughly for a minute. Remove from heat and set aside until cooled.
Shift this pickle to an airtight jar. This pickle can be used for a month or so.