Pat meat dry. Slice into thirds, Freeze for at least 35-40 minutes for easier slicing.
Slice beef against the grain as thinly as you can. Set aside in a large bowl.
In a blender or food processor, blend the onion chunks, garlic, pear, green onion pieces, brown sugar, pepper, soy sauce, and sesame oil until smooth.
Pour the marinade over the beef. Add thinly sliced onion. Mix to coat evenlly. Cover and marinate in the fridge for at least 1 hour or better...overnight.
Drain the beef in a colander over a bowl. Push the meat down a bit to squish excess marinade out. Reserve the marinade for later.
Heat the oil in a large skillet or wok over high heat.
Careful not to crown the pan, sear the marinated beef and onions in batches until browned. Combine all meat, add reserved marinade and cook down for 1-2 minutes.
Turn off heat. Sprinkle with the sliced green onions and sesame seeds.
Serve with rice and or side dishes. (option to toss in steamed veggies, peas & carrots, edamame, broccoli or serve on the side)
