Mix soy sauce, ketchup, vegetable oil, garlic, salt, pepper, and oregano together in a small bowl.

Score both sides of steak in a diamond cut, about 1/8 inch deep. Rub marinade into both sides of the meat. Store in a covered dish or resealable plastic bag in the refrigerator to marinate for 5 to 6 hours, or overnight. Flip meat every few hours.

Preheat an outdoor grill for high heat, and lightly oil the grate.

Place steak on the preheated grill. Cook for 3 to 7 minutes per side, or to the desired doneness.