In a small bowl, mix together garlic, soy sauce, oil, ketchup, oregano, and black pepper. Pierce meat with a fork on both sides. Place meat and marinade in a large resealable plastic bag. Refrigerate 8 hours, or overnight.
Preheat grill for medium-high heat.
Lightly oil the grill grate. Place steak on the grill, and discard marinade. Cook for 5 to 8 minutes per side, depending on thickness. Do not overcook, as it is better on the rare side.