In a mixing bowl, combine soy sauce, brown sugar, sesame oil, rice vinegar, minced garlic, grated ginger, gochujang, chopped scallions, and black pepper. Mix well.

Add the thinly sliced beef to the marinade, ensuring all pieces are coated. Cover and refrigerate for at least 30 minutes, or up to 2 hours for better flavor.

Preheat the grill or pan over medium-high heat. If using a pan, add a little oil to prevent sticking.

Remove the beef from the marinade and cook in batches for about 2-3 minutes on each side, or until browned and cooked through.

Serve the cooked bulgogi over cooked rice, with lettuce leaves and kimchi on the side for wrapping.