Preheat oven to 190°C.
Combine the breadcrumbs, feta cheese, garlic, lemon zest and Italian Herb in a bowl and mix well and season with a little black pepper.
Layer the spinach leaves over the inside of the butterflied leg of lamb and spread the breadcrumb mixture across it.
Carefully roll the lamb up and tie with string at regular intervals to secure.
Place the lamb into the roasting bag and sprinkle seasoning mix over.
Seal the bag with the tie provided and roll gently to coat the lamb evenly.
Pierce the top of the bag 3 times with a sharp knife for the steam to escape.
Place on a baking tray in the centre of the oven and roast for 90-120 minutes. Ensure that the grill is off at all times.
A temperature thermometer inserted into the centre of the roast should read an internal temperature of 70°C.
Cut the bag open, remove the lamb and allow to rest for 10 minutes before carving.