Cut the Onion into small pieces and slice green chillies to long pieces. Grind the coconut well in mixie. Whip the yogurt. Fry mustard seeds in heated oil, add green chillies, curry leaves and onion. Stir for a while and then add the turmeric powder, methi powder, cummin powder and salt. Now add the coconut and a cup of water. Cover it and cook for some time. When cooked well, switch off the stove, and after a while add the yogurt to it, stir well. (Do not add yogurt when it is very hot.) It's ready to use.