Peel or clean the onion, leek, basil, chilli pepper and lemongrass. Then cut into small pieces and fry in a pan. Add the prawns and the fish fillet and briefly fry together. Then add the water and paste. Wash the tomato and clean the mushrooms. Cut both into slices and add them as well. Let it cook until the fish fillet falls apart. At the end, chopped the basil over it. Serve hot.
Note: Be careful with the paste - it can get very hot.