Preheat the oven to 160C/320F/Gas 3.
Mix the harissa paste with the lamb and set aside while you prepare the rest of the tagine. If you have time, it is good to marinate the lamb in the harissa paste overnight in the fridge.
With a vegetable peeler, remove and save the rind of the lemon. Quarter the peeled lemon.
Heat the oil in a casserole dish or tagine on the hob. Brown the marinated lamb and then add the onion, celery, carrot, cinnamon, garlic, turmeric, olives, chickpeas, dried fruit and lemon rind. Place the quartered lemon into the pot. Add the stock, put the lid on the pot and transfer to the oven.
Cook for about 2 hours until the lamb is very tender. Just before serving, top with parsley. Delicious on its own or served with quinoa, brown rice or a crisp green salad.