1. To make the kofta,combine the lamb,onion,cumin,cinnamon,salt and pepper in a bowl and knead with your hands until well mixed. Add egg and mix well. Divide into golfball-size portions and roll into balls.
2. Heat the oil in a large heavy frying pan and cook the meatballs in batches over medium heat until well browned,then set aside. In the same pan,combine the tomatoes,tomato passata,stock,cinnamon,paprika, harissa,sugar,salt and pepper and bring to the boil,stirring. Simmer gently,stirring occasionally,for 15 minutes.
3. Spiralise the zucchini,or use a vegetable peeler to shave the zucchini lengthwise,then slice each shaving into long strips. Add the zucchini to the sauce and cook for 2 minutes until softened,then return the meatballs to the pan and heat through.
4. Scatter with coriander and extra pepper and serve hot.