In a large bowl combine ginger, garlic, turmeric, pepper and yoghurt.
Place lamb in the bowl, mix well, then refrigerate for 2 to 24 hours.
Preheat your oven 325 degrees
Place onions, preppers, chillies, cardamon, cinnammon, paprika, cumin, and coriander in a food processor until fine.
In a large casserole pan, place oil and everything from the food processor and cook over medium heat for 5 minutes, stirring often.
Add tomatoes, then add the marinated lamb, mixing well.
Cover with a tight fitting lid and place in the oven until the meat is tender and the sauce has thickend, approximately 2 hours.
Serve with rice and naan bread