In a slow cooker, add the chicken breast, 1 teaspoon of cumin, the oregano and a large pinch of salt and pepper. Add in the chicken broth and apple cider vinegar. Cover and cook on high for 4 hours.
When there is less than 1 hour left, preheat the oven to 400°F. Halve your poblano pepper and take out the core and seeds. Place the pepper (with the insides facing down) on a baking sheet. Roast in the oven for 20 minutes. Remove and set aside.
Just as the chicken is finishing up, prepare the tinga sauce. In a medium fry pan, add ½ tablespoon of olive oil and the diced yellow onion. Sauté for 2 minutes over medium heat. Then add the canned tomato, the chipotle salsa, thyme and remaining cumin. Mix together and simmer over medium low heat for 5 minutes. Remove from the heat and let cool for a couple minutes. Transfer the sauce to a blender and blend the sauce until smooth. Then pour the sauce back into the pan.
Shred the chicken in the crockpot with two forks - it should fall apart easily. Transfer the chicken to the pan and mix it together with the sauce until well combined and coated. Set aside.
To make the corn salsa, chop up the poblano pepper and place it in a bowl. Add the can of corn, cilantro, red onion, juice of a lime, and a pinch of salt. Mix together with a spoon.
Finally, warm the tortillas. If you have a gas stove, place a tortilla directly on a burner over medium low heat. Let it heat for 10-20 seconds, and then flip it carefully with tongs. Heat until both sides have a few dark scorch marks and the tortilla is crispy (don't heat them for more than 30 seconds per side). Remove from the heat and repeat with the rest of the tortillas.
Assemble! Place a large spoonful of chicken in a tortilla, top with corn salsa and add shredded cheddar on top. If you'd like, add sliced avocado and sour cream. Enjoy!