1. Heat the oven to 200°C/180°C fan oven/gas mark 6. Cut the lamb into large, bite-sized pieces.
2. Put the lamb in a bowl with the onion, turmeric, cumin, potatoes, lemon, mushrooms, and olive oil, and season with black pepper. Stir everything together until coated in the oil and seasonings. Cover and marinate in the fridge for at least one hour. If you prefer, you can do this stage the day before and leave in the fridge overnight.
3. Put a large sheet of foil in a small roasting tin and spoon in the lamb mixture. Bring up the sides of the foil to make a ‘bag’ and pour in the stock. Seal the foil bag tightly.
4. Put the lamb in the oven and immediately reduce the temperature to 160°C/140°C fan oven/gas mark 3. Cook for two hours or until the lamb is meltingly tender. Stir in the coriander. Serve in wholemeal pitta bread with shredded green salad or steamed shredded cabbage and thinly sliced tomatoes.
Or for a faster version...
If you’re in a hurry, the mixture, minus the potatoes, can also be cooked on a foil-lined grill pan, under the grill for 10–12 minutes, turning until golden and tender. Boil the potatoes separately.