In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes.
Stir in the minced garlic and cook for an additional minute until fragrant.
Add the chicken thighs to the skillet and sprinkle with chili powder, cumin, smoked paprika, oregano, salt, and pepper. Stir to coat the chicken evenly with the spices.
Pour in the apple cider vinegar and chicken broth, then add the brown sugar. Bring the mixture to a simmer.
Cover the skillet and reduce the heat to low. Cook for 25-30 minutes, or until the chicken is cooked through and tender.
Remove the chicken from the skillet and shred it using two forks. Return the shredded chicken to the skillet and stir to combine with the sauce.
Warm the corn tortillas in a dry skillet over medium heat for about 30 seconds on each side.
Assemble the tacos by placing a generous amount of the chicken mixture on each tortilla. Top with chopped cilantro and any additional garnishes like radishes and avocado.
Serve with lime wedges on the side for squeezing over the tacos.