Tip the lamb into a bowl with ¼ of the chopped onion, the garlic, ½ tsp cumin, the lemon zest and some black pepper. Mix well with your hands, then shape into 16 small meatballs. Chill for at least 30 mins.
Heat 1 tsp oil in a non-stick frying pan over a medium-high heat. Reserve most of the remaining chopped onion for the salad, then fry the rest for 5 mins until golden. Stir in the remaining cumin, then tip in the rice, bouillon powder, 500ml water and some black pepper. Reduce the heat to a simmer, then cover and cook over a medium heat for 30 mins. Tip in the lentils, cover again and cook for 5-10 mins more until the rice is tender and all the water has been absorbed.
Meanwhile, heat the remaining oil in a non-stick pan over a medium-high heat. Add the meatballs and sliced onion, cover and cook for 5 mins. Stir, then cook for 5 mins more until the meatballs are cooked through and the onions are golden. Stir the tahini and lemon juice together with 3-4 tbsp water to make a sauce.
Mix all of the salad ingredients with the reserved chopped onion. If you're following our Healthy Diet Plan, divide half of the mujadara between two plates and top with half of the meatballs and onions. Spoon over half of the tahini sauce and serve with half of the salad, two lemon wedges and a few mint leaves. Cover and chill the remaining portions to eat another day. Will keep for two to three days in the fridge.