Preheat the oven to 200°C, fan 180°C, gas 6. Mix together 1 tablespoon of the olive oil with 2 teaspoons of the cumin, and brush all over the lamb. Put in a large roasting tin and roast for 1 hour 50 minutes. Remove from the oven and let stand for 10 minutes.
While the lamb is resting, make the spinach. Heat the remaining oil in a large wok or frying pan, add the garlic and remaining cumin, and cook for 30 seconds. Add the spinach and cook, stirring, for 2 minutes until wilted. Stir in the herbs and lemon zest and juice, and season with freshly ground black pepper.
Carve 110g of lamb per person and serve with the herby spinach. Sprinkle the paprika over the yogurt and serve on the side.