The shop had some nice-looking mackerel fillets on offer today so here's how I cooked it - and it was blimmin nice! The combination was deliberately made with the vinegar and onion to balance against the oily mackerel and that worked just great. Serves 2, takes 10 minutes.
Turn the grill on to a medium setting, and put a frying pan on a medium heat.
Chop the onion and start it frying in a good slug of olive oil in the pan. Let it soften while you put the makerel fillets and the tomato (chopped in half) onto some greased foil and then under the grill. The mackerel takes about 10 minutes - put it skin-side down at first then turn it half-way through.
Meanwhile, once the onions have softened a bit, add the vinegar, stir, and turn the heat down to very low so the onions can stew gently.
Mix the lemon zest into the cous cous in a bowl, add boiling water to cover, and put a lid on. Let it stand for about five minutes until everything's just about ready. Then stir the cous cous with a fork before serving it all up.