For the couscous, pour the boiling stock over the couscous, stir and cover with a lid, leave for 5 minutes. Stir again and cover with a lid, leave for a further 5 minutes. Heat the oil, add the onions and cook until soft, add the garlic. Add the spices and cook for a further 3-4 minutes, add the vegetables and cook for 2 minutes. Add the harissa to the vegetables, reduce the heat until the vegetables are cooked and nearly all the liquid has evaporated. Stir in the couscous and mix well together, season to taste and add the chopped coriander. Serve