Preheat the oil in a large nonstick skillet over medium high heat. Season the lamb shanks with salt and pepper, and brown on all sides.
Remove the lamb shanks and put them in the crockpot.
Return the pan to the heat and add the carrots, celery and onion. Saute for 5-7 minutes. Add in the mushrooms and garlic and stir for another minute.
Deglaze with wine and scrape up any of the bits on the pan. Transfer everything to the crockpot. Add the beef stock, mustard, bay leaf, rosemary, and orange rind. Cook on high for 6 hours.
Before serving, stir in the vinegar and season with a pinch each of salt and pepper. Skim off any visible fat from the surface of the sauce and discard. Serve on mashed root vegetables or polenta with some of the cooked veg and sauce.