Remove the lamb from the refrigerator and allow it to come to room temperature for an hour.
Generously season all sides of the lamb with salt and pepper. Place in the roasting rack.
Mix together the olive oil, garlic, rosemary, and lemon zest. Pour over the lamb making sure all the sides are coated.
Let the lamb sit out for an additional half hour to marinate.
Preheat the oven to 400 degrees.
Allow the lamb to roast at 400 degrees for half an hour.
Lower the temperature to 350 and let the lamb roast for an additional 1 1/2 hours, or until the internal temperature is 135-140 degrees for medium rare.