In a large bowl, combine soy sauce, brown sugar, sesame oil, minced garlic, grated ginger, grated Asian pear, half of the green onions, half of the sesame seeds, and black pepper. Mix well until 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, or preferably 4-8 hours for deeper flavor penetration.

Heat a large cast-iron skillet or grill pan over high heat until very hot. Add vegetable oil to coat the surface.

Working in small batches to avoid overcrowding, place the marinated beef slices in a single layer. Cook for 1-2 minutes per side until caramelized and slightly charred at the edges.

Transfer cooked meat to a serving platter. Sprinkle with remaining green onions and sesame seeds while still hot.

Serve hot with steamed rice, lettuce leaves for wrapping, and side dishes of your choice.