Put all the meatball ingredients in a large bowl and use your hands to combine everything together. Roll into about 16 balls, cover and chill until needed.
Heat the oil in a large, deep frying pan over a gentle heat and fry the onion, ginger and spices for 10 mins until the onions are softened. Tip in the tomatoes and a splash of water, and bring to the boil over a high heat. Drop in the meatballs and reduce the heat. Cover and simmer for 15 mins or until the meatballs are cooked. Mix through the yogurt, scatter over the coriander and serve with rice or naan bread.