Spicy barbecued leg of lamb

INGREDIENTS

• 3 sticks lemon grass
• 5 cm piece fresh root ginger, peeled and chopped
• 5 cloves garlic, peeled and chopped
• 6 lime leaves
• 1 good pinch ground cumin
• zest and juice of 1 lemon
• sea salt
• freshly ground black pepper
• 1 quality leg of lamb, boned and butterflied
• a few sprigs fresh mint, leaves picked and finely chopped
• fat-free natural yoghurt
• 1 lemon
• rocket, to serve