Heat the oil in a large frying pan, and fry the onion until golden brown. Stir in the rest of the vegetables, and fry for a few minutes, until coated with oil. Sprinkle on 2-3 tablespoons spice mixture, and stir well to coat the vegetables. Add the water, bring to the boil, partially cover, and simmer for 30-40 minutes. Add the drained chick-peas, and stir in some chopped fresh coriander. Check the seasoning, and add salt if necessary.
Divide the halibut into four equal pieces by removing the centre bone, or cook on the bone, as you wish. Rub 2-3 tablespoons of the spice mixture over the fish. Put the fish in the pan with the vegetables, cover, and let the fish steam for 8 to 10 minutes. Remove from the heat, and transfer the vegetables and fish to a shallow bowl.
For four people, you will need about 400 g (14 oz couscous, to be cooked according to the directions on the packet. This can be done while the vegetables are cooking. Serve the pile of steaming couscous on a serving platter, decorated with coriander leaves and toasted flaked almonds.
For a hint of fruity sharp sweetness to the fish couscous, you can add some chopped pickled lemon or mango chutney.