smash green chillies, ginger and keep it seperate,take a bowl squeeze the tomatos and tamarind with water,add chilli powder and salt.these are said to be the pre preperations... take a pan and pour oil add mustard seeds,fenugreek seeds,curry leaves,smashed green chillies and ginger...saute it...now add the finely chopped onions and saute until it is translucent...now add tuemeric and pour the mixture of tamarind,tomatoes and chilli powder into the pan...allow it to boil well until it thickens...now add fish and stop the flame after 5 mins...final garnish it with coriander leaves...