In a food processor, process pear, onions, garlic, and ginger until pureed (the texture of applesauce).
In a bowl, combine soy sauce, sugar, rice vinegar, sesame oil, salt, and pepper. Stir until sugar and salt are dissolved. Add puree pear mixture, green onions, and sesame seeds. Stir until well-combined.
Add beef, massaging to fully incorporate marinade. Cover with film and marinate in the fridge for 4 hours but not more than 8 hours. Drain beef from marinade.
Over a tabletop grill pan, arrange beef slices in a single layer and cook for about 2 to 4 minutes on each side or until slightly charred and tender.
If using a skillet, add a tablespoon and heat over high heat. Add beef slices and cook, turning as needed, until tender and lightly browned. Serve hot.