1. In a mixing bowl, whisk together olive oil, lime juice, minced garlic, chili powder, paprika, ground cumin, salt, black pepper, oregano, and red pepper flakes.
2. Place chicken in a resealable plastic bag or shallow dish. Pour marinade over the chicken, ensuring it is well coated. Seal the bag or cover the dish and refrigerate for at least 30 minutes, or up to 4 hours for best results.
3. Preheat grill or skillet over medium-high heat. Remove chicken from marinade and cook for 6-7 minutes on each side, or until fully cooked and juices run clear.
4. Let the chicken rest for a few minutes before slicing. Serve with your favorite fajita toppings and tortillas.