Slice ribeye steak into very thin strips and transfer to a large bowl.  

In blender, combine half of the onion with the garlic, pear, green onion, brown sugar, pepper, and soy sauce.  Blend until smooth, then pour over the meat and toss to coat well.  Cover bowl with plastic wrap and refrigerate for 30 minutes to marinate the meat.

In a large pan or cast iron skillet, heat the sesame oil over medium-high heat.  When the oil is hot, add the meat along with the marinade juices and cook, stirring frequently, until the steak is cooked through and the sauce has caramelized.  Sprinkle with additional chopped spring onions or green onions and sesame seeds, if desired.

Prepare the taco sauce by combining all of the ingredients in a bowl and whisking until smooth.  Refrigerate until ready to use.  

Warm the tortillas, then top with the bulgogi beef, kimchi, purple cabbage, cilantro, cilantro and avocado, and garnish with lime wedges, if desired.  Drizzle with taco sauce and serve immediately.