Preheat the oven to 350 degrees F. Salt and pepper the lamb chunks. In a large ovenproof Dutch oven, saute the meat in both oils until browned on all sides. Remove the meat from the Dutch oven and set aside. In the same Dutch oven, saute the celery, leeks and onions until limp, about 3 minutes. Add the cabbage, season with the coriander and thyme and add the tomatoes. Return the meat to the Dutch oven. Add the beef broth, cover and bake until the meat is fork tender, about 2 hours.