Season the swordfish with salt and pepper.
Put the chopped shallots in a food processor with 1 of the garlic cloves, the ginger, turmeric, chilli and 2 tablespoons of the coconut milk. Blend to a smooth paste, scraping the mixture down from the side of the bowl.
Scrape the paste into a large saucepan and add the remaining coconut milk, the curry leaves and sugar. Bring to the boil, then reduce the heat and simmer gently for 5 minutes. Add the fish and cook gently for 10 minutes.
Heat the oil in a small frying pan. Add the sliced shallot, the remaining garlic and the coriander, cumin and fennel seeds and fry gently for 3 minutes. Stir in the chopped coriander, spoon the mixture over the curry and serve.