Season the lamb shanks with salt and pepper. Heat the oil in a large frying pan over a high heat. Reduce the heat to medium, add the lamb shanks and fry for 5–8 minutes until browned on both sides, working in batches to avoid overcrowding the pan and adding extra oil to the pan, if necessary. Use tongs to transfer the lamb shanks to the slow cooker as they brown.
Pour off any excess fat