Chill beef in freezer for 30 minutes to firm it up for easy slicing.
Marinade
Grate Asian pear over a small bowl. Add minced ginger, garlic, low sodium soy sauce, mirin/rice wine, sugar, ground pepper, and sesame. Mix well and set aside.
Using a very sharp knife, slice beef against its grain into very thin slices. Transfer to sliced beef to a medium bowl.
Pour prepared marinade over sliced beef. Allow beef to marinate for 30 minutes.
Heat vegetable oil in a large carbon steel (or cast iron) skillet over medium high heat. Saute sliced onion for 1 minute.
Add marinated beef and stir fry until beef is fully cooked and slightly caramelized, about 7 to 9 minutes.
Transfer to a serving dish and sprinkle with toasted sesame seeds and with sliced green onions.