Put the lentils in a saucepan with the turmeric and stock. Bring to the boil, cover with a tight-fitting lid and simmer for 20-25 minutes, until the lentils are just tender. Remove from the heat and add salt.

Heat the oil  in a small frying pan. Add the cumin seeds and, when they begin to pop, add the ginger and cayenne pepper. Stir-fry the the spices for a few seconds, then pour on to the lentils. Add the lemon juice and the coriander and stir them gently into the mixture.

Lay   the pieces of cod on top of the lentils, cover the pan and then cook gently over a low heat for 10-15 minutes, or until the fish is tender.

Transfer the lentils and cod to warmed serving plates with a fish slice. Sprinkle over the coriander leaves and garnish each serving with one or two lemon wedges. Serve hot.