Ginger-Marinated Hanger Steak

Purée scallions, cilantro, vinegar, gochujang, ginger, soy sauce, sesame oil, pepper, sugar, 1 garlic clove, and 1/4 cup vegetable oil in a blender until smooth. Set aside 1/4 cup marinade and chill. Place steak and remaining marinade in a large resealable plastic bag, turn to coat, and chill at least 2 hours. Remove steak from marinade, scraping off as much marinade as possible. Heat 1 tablespoon vegetable oil in a large skillet over medium-high heat. Cook steak until browned on all sides, 8 –10 minutes for medium-rare (the thinner steaks will cook more quickly). Transfer to a cutting board and let rest at least 5 minutes before slicing. Heat remaining 1 tablespoon vegetable oil in a medium skillet over medium-high heat. Add bok choy, cut side down, and cook until golden brown, about 2 minutes. Turn, add remaining garlic clove, and cook, tossing occasionally, until fragrant, about 1 minute. Add 1/4 cup water and cook until bok choy is tender, about 2 minutes longer. Top steak with chives and serve with bok choy and reserved marinade alongside. DO AHEAD: Steak can be marinated 1 day ahead. Keep chilled.