Slice lamb across grain into 1/2- to 3/4-inch-thick pieces; place in a large bowl. For marinade, stir together the lemon peel, half of the lemon juice, 4 tablespoons of the oil, the oregano, 1/2 teaspoon salt, and 1/8 teaspoon pepper. Cover and marinate at room temperature for 20 minutes. (Or, place lamb in a plastic bag set in a shallow dish. Pour marinade over lamb; close bag. Marinate in the refrigerator for at least 8 hours or up to 24 hours, turning bag occasionally.) In a large bowl combine remaining lemon juice, olives, 1 tablespoon of the remaining oil, the parsley, feta cheese, cinnamon, and 1/4 teaspoon pepper; set aside.
Drain lamb, discard marinade. Brush tomatoes with the remaining 1 tablespoon oil. Grill lamb and tomatoes on the rack of an uncovered grill directly over medium-hot heat for 8 to 10 minutes or until lamb is desired doneness and tomatoes are slightly charred, turning once. Transfer tomatoes to cutting board; cool slightly and slice. Toss the tomatoes with the feta cheese mixture; serve with lamb. Makes 6 servings.