Heat oil in a pan and add mustard seeds, taking care not to burn. When they crackle, add garlic and sauté it till it starts changing colour.Add onion and sauté slowly till it starts turning brown. Add tomatoesand all the spices and cook till sauce is done. Add a little water if the masala becomes too dry - it's all about lowering and increasing the flame when necessary. Add fish, cook for 5 minutes and serve with plain,steamed rice - not pilau - it has its own flavour and can clash with the slightly sour taste of the tamarind fruit. Tilapia is quite a neutral fish, it doesn't have a strong flavour so even people who don't like fish enjoy it. If you prefer a stronger fish, you can substitute salmon. You can even use mackerel, but you'll need to add more tamarind too, so the flavour of the fish doesn't drown the spices. Imli, 167- 169 Wardour St W1, 020 7287 4243, imli.co.uk