Heat olive oil in a large skillet over medium-high 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.
Season the chicken thighs with salt, pepper, chili powder, smoked paprika, and brown sugar.
Place seasoned chicken thighs in the skillet, cooking on each side for about 5-7 minutes until browned.
In a small bowl, mix the soy sauce and apple cider vinegar, then pour over the chicken.
Reduce heat to low, cover the skillet, and let simmer for 10-15 minutes until chicken is cooked through.
Check the chicken's internal temperature, ensuring it reaches 165°F (75°C) for safe consumption.
Remove the chicken from the skillet and let it rest for a few minutes before slicing.
Slice the chicken and serve it garnished with fresh cilantro.