Shredded juicy chicken enveloped in a spicy chipotle tinga sauce makes a great taco filling. I like to roast chicken thighs for shredding because they have the most flavor and maintain their moisture, but you can also shred a rotisserie chicken if you are short on time.
Position a rack in the center of the oven and preheat to 400℉.
Set the chicken thighs inside a Dutch oven or on a baking sheet and coat the chicken with oil. Salt both sides and roast for 40 minutes. It's ok if it's not fully cooked at this stage (you will be cooking it more).
Allow the chicken to cool, then use your hands to tear it into very thin strips. Add the garlic, chipotle peppers, oregano, cumin, tomatoes, and chicken stock to a Dutch oven or casserole dish. Stir and braise in the oven for 20 minutes (uncovered).
Use a skillet over medium heat coated with oil to soften the tortillas, about 20 seconds per side. Stuff the chicken inside the tortillas and top with chopped cilantro, sliced green onion, and sour cream, if desired.