Season the beef with salt and pepper, and let it sit for 10 minutes.

Cut the green onion into small pieces, slice the lemon thinly, and juice the remaining lemon.

Heat salad oil in a pan over medium-high heat, sear the beef for about 1 minute on each side, then wrap it in aluminum foil to rest. Slice the beef into bite-sized pieces once cooled.

In the same pan, heat sesame oil over medium heat, sauté the green onion and garlic until softened. Add lemon slices, lemon juice, salt, and black pepper, and mix well to create the negi sauce.