Method
1. Preheat the oven to 200°C/fan180°C/gas 6. For the fish, make a paste by mixing together the finely grated zest of 1 orange with the cumin, coriander, oil, ginger and some seasoning. Make 3 slashes on both sides of each mackerel, rub the paste inside and over the outside and transfer the fish to a large roasting tin lined with foil.
2. Cut the un-zested orange into round slices and stuff inside each fish. Juice the zested orange and pour over the fish. Bake for 12-15 minutes or until the fish is cooked. A good test is to see if the top dorsal fin comes out easily – if it does, it’s cooked, if not, cook for a further 5 minutes and try again.
3. Meanwhile, put all the couscous ingredients into a large bowl. Pour over 225ml just-boiled water, cover with cling film and set aside for 5 minutes to absorb the liquid. Fluff up the grains with a fork and season to taste with salt and black pepper.
4. Carefully lift a mackerel onto each plate, spooning over the pan juices and rearranging the orange slices inside each fish. Spoon the couscous alongside to serve.