Heat a heavy-based pan over a low heat. Add the spices to the pan then toast for 2-3 mins until fragrant. Crush using a pestle and mortar. Set aside.
Mix the breadcrumbs with 2 tbsp water and the garlic and stir well. Add the lamb, lemon juice, crushed spices, egg most of the mint. Season well. Mix well then shape into 16 balls. Chill for a good 30 mins.
Heat the oil in a frying pan. Fry the balls for 6-7 mins, turning now and then, until golden brown and cooked. Keep warm. Put the couscous in a large heatproof bowl, then rub in the butter and harissa. Pour over 400ml boiling water, cover and leave for 10 mins. Fluff up and season. Shred the remaining mint, then mix through. Serve with harissa and yogurt