To make the marinade, combine the olive oil, orange juice, lime juice, soy sauce, Worcestershire, vinegar, and garlic in a gallon-sized zip lock bag. Seal and shake well. Add the steak, turning to coat. Place in the fridge for 8 hours or overnight. Remove from refrigeration about 1 hour before grilling, if possible.
Preheat the grill to medium heat, 400 degrees F. Grill the flank steak for 10-12 minutes per side, depending on desired level of doneness. Allow to rest on a cutting board before slicing against the grain.
Meanwhile, combine all of the chimichurri ingredients in a food processor or blender and pulse until well-combined but not fully pureed. Serve the chimichurri drizzled over the sliced flank steak.