Rub the lamb with half the harissa paste. Heat the oil in a frying pan and fry the lamb for 3 mins on each side for medium-rare, or a little longer for well-done. Lift the meat out of the pan and tip in the remaining harissa, the dried fruit and nuts, couscous and chickpeas, then stir to coat in the paste. Take the pan off the heat and pour in the stock. Stir briefly, return the lamb to the pan and cover with a lid or tightly-fitting foil for 10 mins until the couscous has absorbed all the liquid.
Fluff up the couscous with a fork, season to taste and fold the mint leaves through to serve.