Heat the oil in a frying pan. Season the meat, brown for approx. 2 mins. on each side, remove from the pan, keep warm.
Heat the oil in the same pan. Stir fry the sweet potatoes for approx. 3 mins., pour in the water, loosen any bits that have stuck to the bottom of the pan, bring to the boil, salt, reduce the heat. Add the couscous, cover and leave to absorb for approx. 5 mins., season. Carve the lamb loin, serve with the couscous.