Prepare a barbecue for medium-high heat. In a large bowl, mix the lamb, breadcrumbs, egg, garlic, cumin, 1 tsp salt and ½ tsp pepper. Divide into 8 balls.
Place the meatballs on 8 metal or soaked bamboo skewers. Shape to form a 2cm-thick, 4cm x 10cm sausage along each skewer, packing tightly. Rub with 1 tbs of the oil. Cook, turning as needed, for 8-10 mins or until browned on all sides and cooked through. Transfer to a serving platter for 5 mins to rest.
Meanwhile, in a medium saucepan over high heat, bring 1 cup (250ml) water, ½ tbs oil and a pinch of salt to boil. Remove from heat. Stir in couscous. Cover tightly and stand for 5 mins or until liquid is absorbed and couscous is tender. Fluff with a fork. Season.
In a small bowl, mix yoghurt, lemon zest and 1 tbs lemon juice. Season with salt and pepper. Arrange couscous and spinach and rocket on a serving platter. Drizzle with remaining 1 tbs oil. Season with salt and pepper. Top with skewers and serve with the sauce.