Add the remaining 1 tablespoon of oil and the onion to the casserole and cook over moderate heat until the onion is softened but not browned, about 3 minutes. Stir in the cinnamon, allspice and 1/4 teaspoon of nutmeg, then the tomato paste. Add the wine and cook, stirring, until the wine is nearly evaporated. Add the lamb along with the tomatoes and their liquid, the tomato sauce, oregano and sugar. Season the lamb mixture with salt and pepper and bring to a boil. Cover and cook over low heat until the lamb is tender, about 1 hour.