Place half the oil in a medium saucepan and heat gently.
Add the onion and a pinch of sea salt and fry for 15-20 minutes,stirring constantly so the onion doesn't stick and burn,or until it turns light brown.
Add the garlic and ginger and fry for a minute or so.
Add the turmeric,cinnamon and cloves and stir for a moment,then add the yoghurt and remove from the heat.
Transfer the onion mix to a blender and purée until smooth. Keep sauce warm.
Heat a barbecue or grill to hot.
Season the lamb with salt and brush with the remaining oil.
Grill the lamb for about 3 minutes on each side or until cooked to your liking.
Rest the lamb for 3-5 minutes in a warm place,then pile the lamb on a plate and sprinkle with coriander,mint and chillies.
Serve the yoghurt sauce on the side.