In a large mixing bowl, combine the soy sauce, sugar, sesame oil, mirin (if using), minced garlic, grated ginger, sesame seeds, and black pepper.
Add the grated pear or apple if using. Mix well until the sugar is dissolved.
Add the thinly sliced beef to the marinade, ensuring all pieces are well coated.
Cover and refrigerate for at least 1 hour, preferably overnight, to allow the flavors to meld and the meat to tenderize.
Heat a large skillet or grill pan over medium-high heat.
Add a little vegetable oil if needed to prevent sticking.
Add the marinated beef, sliced onions, chopped green onions, and julienned carrot to the skillet.
Cook, stirring frequently, until the beef is fully cooked and the vegetables are tender, about 5-7 minutes.
Transfer the bulgogi to a serving dish.
Enjoy your meal!