Alternating, thread 3 pieces each lamb and haloumi onto each skewer, then brush with the oil. Heat a large frypan over medium-high heat. Working in batches, cook skewers for 1-2 minutes each side. Add 1 tbs herbed butter to the pan, then baste skewers and cook for a further 1-2 minutes until charred and glossy. Transfer to a plate and rest, loosely covered with foil, for 5 minutes.