Apply the turmeric powder, chili powder and salt. Leave this for minimum 30 Minutes. If you want to marinate for longer time, then keep the marinated prawns in refrigerator.
For the gravy:
Grind, grated coconut, turmeric powder, tamarind, peppercorns, coriander and red chillies. After grinding the gravy is ready. We will cook prawns in this gravy.
In a kadai, add 1/4 cup water, marinated prawns and chopped radish. Add 2 tablespoon ground gravy to this. Let it cook for 10 minutes.
Pour in the rest of the ground gravy and stir. Add ½ cup water and cook on a medium flame for 2 minutes
Let it get cooked for another 10 minutes switch of the gas.
Now in a tadka/seasoning pan, add oil preferably coconut oil. Once the oil gets heated add chopped onion and fry till it gets burnt. After onion gets burnt, give a tadka of burnt onion to the gravy and close the lid.
Add salt to taste. Remember that the prawns were marinated with salt.
So add only 1/4 teaspoon salt first. Taste and add more if needed.
The gravy should neither be too thick nor too thin.