Heat oil in frying pan and cook the chopped onion and garlic until the onion is translucent. Stir in the curry powder and cook around 4 minutes to mellow the spices.
Add tomatoes, water, and salt; cook 4 minutes more to thicken the sauce.
Meanwhile rinse the fish fillets and arrange in a 1.5-liter flat dish (with lid). Note weight of fish fillets.
Pour tomato mixture over fish in dish. Cover and cook in an 1100-watt microwave on HIGH (100% power) for 4 to 5 1/2 minutes per pound.
Let rest 5 minutes before serving.
Harvey Day, The Complete Book of Curries, 1970
Kiwi Fruit Chutney is a nice accompaniment.
For a fancier version of this dish, see Khari Machhli.http://macheads2.net/recipes/MachhliKaSalna.html