This lamb is the center of a Greek-style supper. Serve it with our Stuffed Zucchini and White Bean Salad.
Preheat oven to 475 degrees. In a blender, puree garlic, oil, oregano, 1/2 teaspoon cinnamon, 1 tablespoon coarse salt, and 1 1/2 teaspoons pepper. Place lamb in a roasting pan; rub with garlic mixture. Roast, turning pan once, 30 minutes. Reduce temperature to 350 degrees; roast, until a thermometer inserted in center registers 130 to 135 degrees, 50 to 60 minutes for medium-rare.
Meanwhile, make yogurt sauce: In a bowl, whisk together yogurt, parsley, and remaining 1/8 teaspoon cinnamon; season with salt and pepper. Refrigerate until ready to serve.
Transfer lamb to cutting board, and tent loosely with foil; let rest 20 minutes. Remove strings from lamb, and cut into 1/2-inch-thick slices. Serve with yogurt sauce.