Dry roast the whole spices until lightly coloured and set aside to cool. Grind finely and stir in the chilli and nutmeg. It can be stored for up to 2-3 months in an airtight jar.
Cut the fish into bite-sized pieces, season with salt and pepper, and set aside.
Heat the oil in a heavy pan and fry the onion until golden. Stir in the massalé and turmeric and lightly fry. Add the pieces of fish, and all the other ingredients. Bring to a simmer and cook for about 10 minutes until the fish is ready.
Serve with rice.