Cut the fish fillet into bite-sized cubes, season with salt and pepper and drizzle with the lemon juice. Wash the coriander and shake dry, coarsely chop the leaves.
Heat the oil in a pan or non-stick saucepan and brown the desiccated coconut over medium heat. Add the coconut milk and mustard and let the sauce boil down creamy in 4 - 5 minutes while stirring. Season with salt and pepper.
Put the fish in the sauce and let it simmer for 1 - 2 minutes. Finally sprinkle with coriander and season to taste.