Heat oil in heavy extra-large deep skillet or flameproof casserole over medium-high heat. Dredge shanks in flour; shake off excess. Add to skillet and cook until brown, turning occasionally, about 12 minutes. Transfer shanks to bowl. Reduce heat to medium-low. Add onion and garlic and saute until tender, about 4 minutes. Return shanks and any liquid in bowl to skillet. Season shanks with salt and pepper. Add tomatoes, broth, wine, basil and lemon peel to skillet. Cover partially and simmer until veal is very tender and begins to fall off bones, about 2 hours. (Can be prepared 3 days ahead. Cover and refrigerate. Simmer 10 minutes over medium heal before continuing.) Ladle into bowls and serve with Gremolata.