Grind the cashew nuts, mustard seeds, green chilies and coconut to a smooth paste. Mix along with yoghurt, salt, turmeric powder, mustard oil, coriander leaves and prawns. Marinate for 10 minutes.
Heat a tawa and place the banana leaves on them for a few seconds on both sides. This will help it to become more pliable so that it can be easily folded without breaking. Place little of the prawn mix in the centre of a banana leaf along with a chilli and fold.
Tie with a string and keep aside. Do the same with rest of the prawns mix. Steam for 15 minutes. Midway, turn them over gently to cook the other side too.
Serve them with hot steamed rice.
