For the BULGOGI:
Pop the steak in the freezer for 15–30 minutes, just until firm enough to slice thinly against the grain. Blend the remaining bulgogi ingredients (Asian pear, onion, garlic cloves, grated ginger, chopped scallions, soy sauce, sugar, toasted sesame oil, black pepper) together. Toss the blended marinade with the beef and refrigerate for at least 30 minutes while you make the tortillas.
For the TORTILLAS:
In separate bowls, mix each packed cup of masa harina (blue corn and white corn) with 1 scant cup warm water. Knead each dough until soft and pliable, adding a little more water if the dough cracks or masa harina if it's sticky. Take a small ball of each color, gently roll them together, and press between two sheets of plastic for a yin-yang effect. Peel off the plastic and cook on a hot, dry griddle on both sides. Keep cooked tortillas covered with a clean towel.
To Assemble:
Grill the marinated beef in batches until browned and caramelized. Melt shredded Oaxaca cheese onto the tortillas, then pile on the bulgogi and chopped kimchi. Garnish with sliced scallions if desired.
