Sauté the onions in the oil in a heavy saucepan until lightly golden. Add garlic, ginger, cumin, coriander, chillies, cardamom and turmeric and fry gently for 2 minutes. Add lamb and coat with the onion and spice mixture. Stir in the yoghurt, cover and simmer gently for 45 minutes, stirring occasionally or cook in the oven, Gas Mark 4, 180°C (350°F) for approximately 1 hour.
Add mushrooms and continue cooking for a further 15 minutes or until the lamb is tender. Stir in the lemon/lime juice, season with salt and black pepper. Garnish with a sprig of coriander or chervil and a fresh red chilli cut in half.