Place sliced beef tenderloin in medium bowl. Using a food processor or blender combine the onion, garlic, and Asian or Bosc pear until pureed then pour over sliced beef tenderloin.
In a small bowl add soy sauce, brown sugar, sesame oil, sliced carrots, salt, and pepper and mix thoroughly, then pour over the beef tenderloin mixture. Cover with plastic wrap and place in refrigerator for at least 1 hour to overnight.
After marinating, heat 1 tbsp vegetable oil in a large pan over medium-high heat and cook the beef in batches until cooked through, around 6-8 minutes OR cook on a hot grill until cooked through and lightly charred.
Serve immediately, garnished with sliced green onions. You can eat the bulgogi with rice, in lettuce wraps, or even in tacos.