Score the skin of the pork loin if it isn't already. Pat dry with kitchen paper.
Combine the oil, lemon zest, sage, salt and pepper. Rub it all over the pork loin. Roll it up tightly and secure with kitchen string. Place in the fridge to marinate while you prepare your barbecue (you can do this the night before and marinate overnight, if desired).
Follow your barbecue's instructions for a rotisserie to preheat to medium high. Remove your barbecue's rotisserie rod (spit) and skewer the pork loin through the centre, securing with the prongs of your rotisserie rod.
Once the barbecue is preheated, load the rod onto the rotisserie motor. Place a tray covered with aluminium foil underneath to catch any drippings.
Cook for about 1 hour and 40 minutes, or until the centre of the pork loin is no longer pink and reaches 63 degrees C on a meat thermometer. Let the pork rest for 10 minutes before slicing.
Roast your vegetables while the pork is cooking on the rotisserie. Simply arrange a single layer of vegetables on the foil-lined tray. The veg will cook and also roast in some of the delicious pork dripping, taking on loads of flavour. Some ideas are: broccoli florets, Brussels sprouts, shallots, onion wedges, cauliflower florets, potatoes, etc.