Add the onions, carrots, celery and garlic to the casserole and cook over low heat, stirring, until the vegetables start to brown, about 8 minutes. Raise the heat to high, add the tomatoes and boil until the juices evaporate, about 4 minutes. Add the wine and boil for 3 minutes. Add the chicken stock, parsley, thyme, marjoram and orange zest and bring to a simmer. Return the lamb to the casserole, cover and bake for about 4 hours, or until the meat is very tender and falling off the bone.