Heat 2 tablespoons of olive oil in a large non-stick frying pan over high heat. Cook lamb, turning for 2-3 minutes. Transfer to a 4.5 litre (18-cup) slow cooker.
Heat another 2 tablespoon oil in the same pan over medium heat. Add the onion, fennel and celery. Cook, stirring occasionally, for 2-3 minutes. Add the garlic, rosemary and lemon zest, and cook, stirring, for 1 minute. Add lemon juice and white wine, and simmer for 2 minutes. Add stock and ½ cup of water, and bring to the boil. Transfer the mixture to the slow cooker.
Cook, covered, on high for 4 hours (or low for 8 hours), or until the lamb is very tender and falling off the bone. Add the cannellini beans for the last 30 minutes of cooking time.
When ready to serve, heat the remaining oil in a large non-stick frying pan over high heat. Add kale. Cook, tossing with tongs, for 2-3 minutes, or until kale is wilted. Serve the shanks with the wilted kale.