In a small bowl, whisk together the oil, lime juice, chili powder, cumin, garlic powder, oregano, salt, black pepper, and red pepper flakes.
Place the chicken in Ziploc bag with the fajita marinade. Seal the bag and make sure all of the chicken pieces are well coated. Place the bag in the refrigerator for at least 1 hour and up to 8 hours.
When ready to cook, preheat the grill to medium-high heat. Thread marinated chicken, onion, and peppers onto skewers. Discard leftover marinade.
Lightly oil the grill grate. Place the kabobs on the grill, cover, and cook until the chicken is opaque throughout, about 8-12 minutes, turning once or twice during cooking. Transfer to a warmed platter and serve immediately.
Note-if using wooden skewers soak them in water 20 minutes before using.