Heat oil in a large, deep cast iron skillet or stainless steel skillet over medium heat. Season both sides of the chicken thighs with salt, pepper, and smoked paprika and add them to the hot skillet. Sear the chicken for 4-5 minutes on each side. Transfer chicken thighs to a plate.
2 tablespoons light olive oil, 1 ½ pounds boneless, skinless chicken thighs, ½ tablespoon smoked paprika, 1 teaspoon kosher salt, ½ teaspoon black pepper
Add the onions to the skillet and cook until softened and beginning to brown. Then, stir in the garlic, chipotle peppers, and ketchup and sauté for an additional 1-2 minutes.
½ large white onion, 1 clove garlic, 1-2 chipotle peppers in adobo sauce, 1 tablespoon ketchup
Pour in the chicken stock, scraping the bottom of the pan to remove any fond that built up. Add the chicken and its juices back to the skillet. Spread the chicken thighs out evenly in the skillet and cover it with a lid. Braise for 45-60 minutes or until the chicken is very tender.
1 cup chicken stock
Remove the chicken to a plate and shred it with two forks. Add the shredded chicken back to the skillet and continue simmering until most of the liquid has evaporated. Serve on flour tortillas with guacamole, salsa, cheese, and any other toppings you like!
8 small flour tortillas