Trim the fat from steak. Score steak on both sides by making shallow cuts at 1 inch intervals in a diamond pattern.
Place steak in a plastic bag set in a shallow dish. For marinade, combine the lemon zest, lemon juice, sugar, soy sauce, oregano and pepper.
Pour over steak, seal bag. Marinate in refrigerator for 2 to 24 hours, turning bag occasionally.
Drain steak, preserving the marinade. Grill steak on an uncovered grill directly over medium heat for 17 to 21 minutes for medium, turning and brushing marinade once over the steak halfway through cooking.
To serve thinly slice steak diagonally across the grain.