Preheat oven to 350° F.
Cut open dried chiles and remove seeds.
Roast dried chiles on a pre-heated cast-iron skillet for approximately 20-30 seconds per side. Chiles will begin to have a fruity smell and darken, resembling leather. Be careful not to over toast. Tear or cut the toasted chiles into pieces.
In a medium saucepan simmer the chicken stock, apple cider vinegar, and roasted dried chiles for 10 minutes.
Pour the chicken stock, chiles, Mexican oregano, garlic powder, kosher salt, and ground cumin into a blender and blend until smooth.
Place the chicken thighs in a baking dish and cover with the chile sauce.
Bake for 40-45 minutes or until chicken is able to be shredded with a fork.
Shred chicken with a fork or rough chop then let it sit in the chile sauce for 5-10 minutes prior to preparing tacos.
Over an open gas stovetop flame on medium/low heat corn tortillas until lightly charred on the edges (approximately 10 seconds per side). Stack together 2 tortillas and place 1-2 tablespoons of chicken in each taco. Top with chopped cilantro, red onion, and a sprinkling of cojita cheese. Serve with a few slices of limes and a side of avocado or guacamole.