In a large mixing bowl, toss together 1½ pounds of thinly sliced boneless ribeye and ½ small yellow onion. Set aside.

In a blender, combine soy sauce, brown sugar, mirin, sesame oil, black pepper, Asian pear, garlic cloves, and minced ginger. Blend until smooth.

Pour the marinade over the beef and onion mixture and coat evenly. Cover and refrigerate for at least 6 hours.

Heat a skillet over medium-high heat and add vegetable oil. Cook half of the marinated beef and onion for 4 to 6 minutes.

Remove cooked beef and repeat with remaining beef and onion with more oil.

Return all beef and onion to skillet, toss gently to combine, and serve garnished with green onions and sesame seeds.