1. Combine first 4 ingredients in a small bowl; add 3/8 teaspoon salt. Rub spice mixture over lamb. Arrange lamb in a 13 x 9-inch glass or ceramic baking dish. Combine yogurt and garlic. Spread half of yogurt mixture over lamb. Cover and marinate lamb mixture 8 hours or overnight.
2. Combine remaining yogurt mixture, oil, and remaining 1/8 teaspoon salt. Cover and chill.
3. Preheat oven to 425°.
4. Remove lamb from refrigerator; let stand, uncovered, 30 minutes. Remove lamb from dish, and place on a jelly-roll pan. Bake at 425° for 22 minutes or until a thermometer inserted in thickest part of lamb registers 130°. Preheat broiler to high. Add tomatoes to pan with lamb. Broil 1 minute or until lamb is browned and tomatoes start to blacken. Let stand 5 minutes. Serve with yogurt sauce.