Leg of lamb stuffed with couscous

Ingredients

• 200g couscous
• 300ml boiling water
• Large handful fresh parsley, finely chopped
• Small handful fresh mint, finely sliced
• 1 lemon, zest only, finely grated
• 25g pistachios, finely chopped
• 1 clove garlic, peeled and finely chopped
• Freshly ground black pepper
• 500g half leg of lamb, butterflied
• 2 sprigs rosemary
• 1 onion, sliced into rounds
• 400g carrots, peeled and quartered lengthways
• 250g asparagus, woody ends removed