Serves 16 (serving size: about 3 ounces lamb, 1/3 cup vegetables, 2 teaspoons herb mixture, and 1 tablespoon jus)
1. Combine first 8 ingredients in a medium bowl. Add 1 teaspoon salt to spice mixture. Rub spice mixture evenly over lamb. Reroll roast; secure at 1-inch intervals with twine. Wrap in plastic wrap; refrigerate 6 to 24 hours.
2. Preheat oven to 375°.
3. Remove lamb from refrigerator; let stand at room temperature 30 minutes. Place lamb on a wire rack; place rack in a roasting pan. Pour 4 cups water into pan. Roast lamb at 375° for 1 hour and 45 minutes or until thermometer registers 130°. Remove from oven. Let stand at room temperature 20 minutes; cut across grain into thin slices.
4. Place drippings from pan in a small saucepan over high heat; bring to a boil. Cook until reduced to 1 cup.
5. Combine onion and next 5 ingredients (through 1/2 teaspoon pepper) in a small bowl. Stir in 1/2 teaspoon salt.
6. Combine remaining salt, parsnips, and remaining ingredients in a bowl; toss to coat. Serve with lamb. Top lamb with herb mixture; drizzle with jus.