Heat a frying pan over a medium heat. Add the cumin and coriander seeds and toast until they start to make a popping sound, about 2 minutes. Remove from the heat and whizz until smooth in either a grinder or crush in a pestle and mortar.
Heat the oil in a large frying pan over a medium heat. Add the onions and pepper and cook for 3-4 minutes or until softened. Add the garlic, chilli and spices and cook for a further 2 minutes.
Add the tomatoes, vinegar, sugar, salt and pepper and coriander. Fill the tomato tin with water, swirl and tip into the frying pan. Bring to the boil, reduce the heat and stirring regularly simmer gently for 5-10 minutes, or until the sauce has thickened.
Meanwhile, heat the sunflower oil in a medium frying pan. Add the meatballs and cook for 5-10 minutes, or until golden all over. Add the meat balls to the sauce and simmer gently for a further 10-15 minutes, stirring from time to time, or until cooked through. Transfer to a large warmed platter. Garnish with chives and coriander. Serve with couscous and warmed pitta breads.