Heat oil in a pan*.Once hot, add the mustard seeds, ginger,garlic,chillies and the curry leaves.Saute for 30 seconds.
Add the finely chopped onions next.Cook till it's golden brown.
To this, add the chopped tomatoes and cook for 5 more minutes till the tomatoes start disintegrating and loosing shape.Add more water if the pan is getting too dry.
Add the cleaned prawn along with turmeric and salt.Mix gently without breaking the prawn till both sides turn pink.
After the prawn turns pink on both the sides,Add the prepared coconut masala.Mix well to evenly coat all the prawn.
Cook for another 10 minutes till the coconut masala becomes dry and prawns roast.
Check the salt, chilli and sourness- adjust accordingly.
Garnish with coriander and serve hot.