Combine 1/2 tablespoon olive oil, balsamic vinegar, chili powder, paprika, garlic powder, and onion powder in a large resealable plastic bag. Season with salt and pepper. Add chicken thighs. Seal bag and shake until chicken thighs are evenly coated.

Marinate in the refrigerator, 15 to 30 minutes.

Heat remaining oil in a skillet over medium heat. Add onion and garlic; saute until fragrant and translucent, about 5 minutes. Add chicken thighs to the skillet. Cover and cook until inside is no longer pink and juices run clear, about 25 minutes.