Cut the hot dog bun using a bread knife with a serrated edge in the middle of the bun. Spread butter inside the bun then toast it briefly. Then set aside.
Heat a pan with a little oil, then sauté onions, garlic, and green bell peppers until fragrant. Add minced beef, bulgogi sauce, worcestershire sauce, salt, and black pepper. Add mozzarella cheese, then stir until well combined.
Add lettuce slices into the bun, then top it with the bulgogi beef mixture. The cheese bulgogi beef sandwich is ready to serve. Enjoy!