In the work bowl of a food processor, pulse together parsley, chives, oil, lime juice, rosemary, oregano, garlic, 1 teaspoon salt, 1 teaspoon pepper, and cumin until herbs are finely chopped. Transfer mixture to a small bowl. Stir soy sauce, Worcestershire, and sugar into herb mixture. Reserve half of herb mixture in another bowl; cover and refrigerate.
In a large resealable plastic bag, combine steak and remaining herb mixture; seal bag, turning to coat steak. Refrigerate for 1 to 2 hours.
Preheat oven to 350°. Let steak and bowl of reserved chimichurri stand at room temperature for 15 minutes. Heat a two-burner cast-iron grill pan over medium heat until hot, 8 to 10 minutes.
Remove steak from bag, discarding marinade. Sprinkle steak with remaining ½ teaspoon salt and remaining ½ teaspoon pepper. Cook steak until well browned, 2 to 3 minutes per side. Transfer pan to oven.
Bake until an instant-read thermometer inserted in thickest portion of steak reads 130°, 10 to 12 minutes. Let steak stand for 5 to 10 minutes. (Temperature will continue to rise about 5 degrees.) Slice across the grain; serve with reserved sauce and lime.
Recipe by Southern Cast Iron at https://southerncastiron.com/herb-marinated-flank-steak/