Place deboned lamb in a roasting pan and rub all over both sides with the garlic-olive oil mixture. Squeeze the juice from the lemons over the lamb. Let marinade, refrigerated, at least 1 hour but it's best if you can marinade it overnight. If you do marinate overnight, take the meat out of the fridge about 30 minutes before cooking.

Pre-heat a grill to high heat. Place the lamb on the hot grill and sear on each side for 5-7 minutes. Turn the heat down to medium and cook, turning often, for another 35-40 minutes. If the grill has a cover, close it during cooking to roast the inside.

Check for doneness by cutting into the thickest part of the meat. For medium, the lamb will be pink in the center. Return it to the grill if necessary. When done to your liking, remove from grill and let stand for 10 minutes before carving. Carve into thin, delicious slices and serve immediately.