Roast Leg of Lamb with Potatoes, Artichokes and Olives

Finely mince 1/2 cup oregano, garlic, salt and pepper in processor. Place lamb in large roasting pan. Rub lamb with 2 tablespoons olive oil. Spread 4 tablespoons oregano mixture over lamb, reserving remainder. Arrange lamb so that fat side is up. Let stand at room temperature 1 hour. Meanwhile, fill large pot with cold water. Add 4 tablespoons lemon juice to water. Cut 1 artichoke lengthwise into 8 wedges. Rub cut surfaces of artichoke with lemon half to prevent discoloring. Cut away choke and discard, leaving artichoke wedges intact. Place artichokes in pot with water . Repeat with remaining artichokes. Boil artichokes until almost tender, about 15 minutes. Drain. Transfer to large bowl. Add olives, 1 tablespoon lemon juice and 1 teaspoon oregano mixture to artichokes; toss to coat. Set aside. Preheat oven to 450 °F. Roast lamb 10 minutes. Reduce temperature to 350 °F. Meanwhile, mix potatoes, 2 tablespoons oil and oregano mixture in bowl. Arrange potatoes around lamb in roasting pan. Roast until thermometer inserted into thickest part of lamb registers 140 °F, about 50 minutes. Transfer lamb to large platter. Add artichoke mixture to roasting pan with potatoes; mix well. Continue roasting vegetables until tender, about 20 minutes. Surround lamb with vegetables. Garnish with oregano sprigs and carve roast at table.