Insert eight sage leaves all around the roast under the strings. Season with salt and pepper. In an ovenproof skillet, brown the roast in the oil. Add the lemon zest and garlic and roast in the oven for about 25 minutes or until a thermometer in the centre of the roast reaches 52 °C (125 °F). Remove the roast from the skillet and set aside on a plate for about 10 minutes. The internal temperature of the meat should climb to 55 °C (130 °F) for medium rare.