Mix all of the ingredients, except for the chicken, scallions, and sesame seeds, in a large bowl. Add the chicken, stirring until it is well coated with the marinade. Cover and refrigerate for 2 to 3 hours.
Preheat the oven to 375°.
Spread the chicken out on a large baking sheet, and bake it for 30 minutes, and then broil it until browned. Watch it closely, because it can burn quickly. Take the chicken out of the oven, slice it, and sprinkle it with the scallions and sesame seeds.
Toast the tortillas in a cast iron pan until they're browned. Fill with chicken, and top with gouchujang mayonnaise and pickled slaw.
For the Gouchujang Mayonnaise:
Mix all the ingredients in a small bowl, and cover and refrigerate until serving time.
For the Pickled Slaw:
In a large bowl, mix together the vinegar, sugar, and salt.
Add the vegetables and stir well. Cover and refrigerate until serving time.