Pat the lamb dry. In a small bowl, stir the garlic, olive oil, rosemary, thyme, lemon zest, salt and pepper into a thick paste.

Rub the paste over the lamb, working it into any folds. Let sit at room temperature for 45 minutes, or cover and refrigerate up to overnight.

If refrigerated, set the lamb out 45 minutes before roasting so it is not cold in the center.

Preheat the oven to 450°F. Set the lamb on a rack in a roasting pan.

Roast for 20 minutes, then reduce the oven to 325°F without opening the door.

Continue roasting for 55 to 65 minutes, until a thermometer in the thickest part reads 130°F for medium-rare.

Transfer to a cutting board and tent loosely with foil. Rest for 15 minutes, the temperature climbs to about 135°F.

Remove the twine and slice thin against the grain, fanning the slices on a platter.