Marinate chicken thighs with ingredients mentioned under Taco marinade. Let it rest for 30 minutes.
Heat oil in a cast iron pan, sear chicken upside down for 4-5 minutes on medium heat. Flip and cook for another 4-5 minutes until you see clear juice running down the chicken and it is cooked through.
Cover and rest the chicken for 10 minutes. Let it cool down. Shred or cut chicken thighs into bite-sized pieces.
To the same cast iron pan, add chopped onion, tomato paste, and chipotle in adobo sauce. Saute for a minute.
Add chicken stock to the pan and mix.
To the skillet add chicken thigh and mix everything well. Let it simmer for a minute for the sauce to come together. (ref note -2)
Heat another skillet. Lightly grease with oil. Place a tortilla. Sprinkle about 1-2 tablespoons of cheese and top it with about 2 tablespoons of chicken taco filling.
Fold the taco over and press down with a spatula. Continue cooking until the taco is crisp and golden on the bottom, about 2-3 minutes. Then flip and continue cooking the other side. (ref note 3)
Repeat the above step for the rest of the tortillas.
Serve chicken taco with pico de gallo, guacamole, and other accompaniments.