Mix the barbecue sauce, garlic, chili powder, tomato puree, lemon juice, and half of the chopped onion in a bowl.
Let the chicken marinate in this mixture for at least an hour in the refrigerator.
Preheat your oven to 375°F (190°C).
Meanwhile, heat olive oil in an oven-safe skillet over medium heat.
Add the marinated chicken, skin-side down, for about 2-3 minutes until lightly browned.
Turn the chicken over and brown the other side for another 2-3 minutes.
Add remaining marinade into the skillet.
Transfer the skillet to the preheated oven and bake the chicken for 30 minutes.
Ensure the chicken is cooked through and reaches an internal temperature of 165°F.
Remove the chicken from the oven and allow it to cool slightly.
Use two forks to shred the chicken.
Mix back into its juices and serve hot.