1. In small bowl, whisk marinade, 1 teaspoon oregano, lime zest and orange zest. Place steaks in large zip-top plastic bag; pour marinade mixture over steak. Seal bag, pressing out excess air; massage steak in bag to coat. Refrigerate steak at least 4 or up to 10 hours.
2. In food processor with knife blade attached or blender, purée garlic, onions, parsley, cilantro, vinegar, lime juice, salt and remaining 1 teaspoon oregano; with processor running, slowly pouroil through feed tube and purée until emulsified. Makes about 1 cup chimichurri.
3. Prepare outdoor grill for direct grilling over high heat. Remove steaks from marinade; discard marinade. Place steaks on hot grill rack; cover and cook 8 minutes or until internal temperature reaches 135° for medium-rare, turning once. Transfer steaks to cutting board; tent with foil and let stand 5 minutes. (Internal temperature will rise to 145° upon standing.)
4. Slice steaks against the grain; serve with chimichurri.

Approximate nutritional values per serving (1 piece steak, 2 1/2 tablespoons chimichurri): 333 Calories, 21g Fat, 5g Saturated Fat, 86mg Cholesterol, 522mg Sodium, 4g Carbohydrates, 1g Fiber, 0g Sugars, 0g Added Sugars, 31g Protein