Place the onion, ginger and garlic in a food processor and pulse until you have a paste. Heat the vegetable oil in a large casserole dish over a moderate heat until hot. Fry the whole spices for a few minutes, stirring occasionally. Add the onion, garlic and ginger paste to the dish, stirring frequently, for 3-4 minutes until it starts to turn golden in colour. Add the chopped tomatoes to the dish and cook for a few minutes. Add the diced lamb then sprinkle over the spices and a little seasoning, stirring well. Add enough water to cover the meat, then bring the mixture to a simmer. Reduce the heat to low, cover the dish and cook for 60-70 minutes, stirring occasionally, until the lamb is tender and breaks apart easily in your hands. Remove from the heat and stir through the spinach until wilted. Adjust the seasoning to taste. Spoon into serving bowls and serve.
