Cook the kale in boiling water until just wilted, then refresh in iced water. Drain and carefully squeeze the excess water from the kale, then roughly chop. Tip into a mixing bowl, stir in the garlic, anchovies, zest and breadcrumbs, and season (add lots of pepper). Pack the stuffing into the cavity of the lamb and tie with string – it doesn’t matter if it’s messy, just make sure the filling is secured. Can be prepared up to a day ahead and kept in the fridge.