In a large frying pan, sauté the onions in olive oil. Once the onions begin to brown add lamb cubes. Simmer on low and allow to cook for about 30 minutes. In the meantime, puree the pomegranate seeds in a food processor and add the beef stock. Pour into a bowl and add the walnuts, and sugar. Pour this mixture into a medium to large saucepan and heat over low heat. Bring to a boil and reduce heat to simmer for 10 minutes. Once the lamb is done simmering, drain fat and juices. Add the spices and mix well. Allow the lamb and spice mixture to simmer for 15 minutes. Add pomegranate sauce and cook on low for about 20 minutes. Serve hot with steamed Basmati rice. Sprinkle toasted walnuts on top for garnish. Makes 4 to 6 servings.