Pre-heat the oven to Gas Mark 4, 180°C (350°F).
Cover the bulgur wheat with 50 ml of boiling water and set aside to allow it to absorb the water.
Heat the oil in frying pan over a low heat. Add the garlic and cook for 2 minutes. Add the harissa, stir for 30 seconds, then add the tomatoes, sugar and salt and pepper. Simmer gently while you prepare the meatballs.
Mix the minced lamb with the bulgur wheat, egg, chopped coriander, cumin and salt and pepper. Roll into meatballs the size of a walnut and place them in an oven proof dish. Cook in the oven for 10 minutes.
Remove from the oven and pour the sauce over the meatballs. Stir gently to combine. Sprinkle with mozzarella followed by cheddar. Cook in the oven for 10 minutes until golden brown.