Trim fat from meat. Score meat on both sides by making shallow cuts at 1-inch intervals in a diamond pattern. Place meat in a resealable plastic bag set in a shallow dish. For marinade, combine the lemon peel, lemon juice, sugar, soy sauce, oregano, and pepper. Pour over meat; close bag. Marinate in the refrigerator for 2 to 24 hours. Drain meat, reserving marinade.
Preheat broiler. Place meat on the unheated rack of a broiler pan. Broil 4 to 5 inches from the heat for 15 to 18 minutes for medium (160 degree F), turning and brushing once with marinade halfway through broiling. Discard any remaining marinade.
To serve, thinly slice meat diagonally across the grain. If desired, garnish with lemon slices and fresh oregano leaves. Makes 6 servings.