Preheat oven to 160°C(315°F). Heat oil in a heavy-bottomed casserole dish. It should be big enough to fit the shanks in a single layer. Lightly dust the shanks in the flour and brown in casserole dish. Remove from dish.
Add onion and cook gently for a few minutes. Stir in garlic, celery, carrot and parsnip. Pour in wine and let come back up to heat, about 1 minute. Return the shanks to the dish. Add the stock, passata herbs and orange peel. Cover and bake for 2 hours or until shanks are tender.
Gently remove the shanks from the dish and arrange on a warm serving plate. Spoon the vegetables and gravy over the shanks. Discard herbs. Serve with the polenta.
Polenta: Bring the stock and water to the boil. Slowly rain in the polenta, stirring constantly. Reduce heat and simmer over low heat for 5-6 minutes or until mix starts to leave the side of the pot. Remove from heat, add butter and season with salt and pepper. Spoon into a warm serving dish.