In a small bowl, whisk gochujang, vegetable oil, vinegar, soy sauce, honey, and garlic until smooth.
Place skirt steak in a sealable plastic bag and pour marinade over top. Seal bag and place in refrigerator to marinate for 2 hours or up to 12.
Lightly oil the grates on a grill and preheat to 425F. Remove steak from marinade (do not discard marinade) and lightly pat dry.
Place steak on preheated grill and grill 3-4 minutes on each side until internal temperature of steak reaches 130-135F for medium-rare (see blog post for additional cook preferences)
Place steak on a cutting board, lightly tent with foil, and allow to rest 10 minutes. Meanwhile, bring marinade to a simmer in a small saucepan over medium-high heat. Reduce heat to medium and let cook 3-4 minutes until slightly reduced, stirring occasionally.
Thinly slice steak against the grain and arrange on a serving platter. Drizzle gochujang sauce over top and garnish steak with green onion and sesame seeds. Enjoy!