In a medium bowl, combine soy sauce, sesame oil, honey, gochujang, grated ginger, minced garlic, rice vinegar, and black pepper. Whisk until well blended to create the marinade.
Add the thinly sliced beef sirloin to the marinade. Toss to coat all pieces evenly. Cover and refrigerate for at least 1 hour, preferably 2 hours for maximum flavor.
Preheat a grill or grill pan over medium-high heat.
Remove beef from marinade, letting excess drip off. Grill the beef slices in batches for 2-3 minutes per side or until cooked through and slightly charred.
Transfer grilled beef to a serving platter. Sprinkle with sliced green onions and toasted sesame seeds.
Serve immediately with steamed vegetables or rice as desired.