Thinly slice steak across the grain; transfer sliced steak to a large zip top bag. You can also use a large mixing bowl.
To the zip top bag add grated pear, soy sauce, garlic, gochugaru, ginger, brown sugar, and sesame oil; seal the bag and squish everything around to completely coat the meat with the marinade.
Let sit at room temperature for 1 hour, OR put in the fridge for up to 8 hours.
When ready to cook, heat up 1 tablespoon vegetable oil in a grill pan or cast iron skillet set over medium-high heat.
Remove one-third of the steak slices from the marinade and add to the hot oil in a single layer; cook for 1 to 2 minutes, or until browned.
Flip over and continue to cook for 2 more minutes, or until browned with crisp edges. Stir occasionally. Cooking time will depend on the thickness of the steak.
Transfer cooked pieces to a plate and repeat the above cooking steps with remaining oil and steak.
Garnish with chopped green onions and sesame seeds.