Trim fat from meat. Cut lamb across the grain into 1/2- to 3/4-inch slices. Place lamb in a large resealable plastic bag set in a shallow dish. For marinade, in a small bowl stir together lemon peel, 1/3 cup of the lemon juice, 4 tablespoons of the oil, the oregano, salt, and the 1/8 teaspoon pepper. Pour marinade over lamb; seal bag. Marinate in the refrigerator for 8 to 24 hours, turning bag occasionally.
In a large bowl combine remaining lemon juice, 1 tablespoon of the remaining oil, the parsley, feta cheese, olives, cinnamon, and the 1/4 teaspoon pepper; set aside. Drain lamb, discarding marinade. Brush tomatoes with remaining 1 tablespoon oil.
For a charcoal grill, grill lamb and tomatoes on the rack of an uncovered grill directly over medium coals until meat is desired doneness and tomatoes are slightly charred, turning once halfway through grilling. (Allow about 8 minutes for medium-rare (145 degrees F) or about 10 minutes for medium doneness (160 degrees F). (For a gas grill, preheat grill. Reduce heat to medium. Place meat and tomatoes on grill rack over heat. Cover and grill as above.)
Transfer tomatoes to a cutting board; cool slightly and slice. Toss tomatoes with the feta cheese mixture. Serve lamb with tomato mixture. Makes 6 servings.