Mix the lemon juice and the jalfrezi curry powder in a large bowl. Add the chopped lamb and stir to coat well. Leave to marinate for at least 1 hour, but overnight if possible.

In a large heavy based pan, heat the oil over a medium heat. Add the onions and fry until transparent. Add the garlic and continue to cook for a further 2 minutes. Turn up the heat and add the lamb. Cook to brown on all sides. Add the tomato puree and cook for 2 minutes. Add the tomatoes and peppers. Stir well, then turn down the heat and allow the lamb and tomatoes to cook covered for 30 minutes. Stir frequently. Don’t allow the lamb to catch on the bottom of the pan – add a little water if necessary. Once the lamb is cooked and the tomatoes have broken down, add the garam masala and the chopped green chilli if using. Season with salt and pepper and cook for a further 3-4 minutes before serving.