In a large mixing bowl, whisk together olive oil, chili powder, cumin, paprika, garlic powder, onion powder, black pepper, cayenne pepper (if using), lime juice, and salt.

Add the chicken breasts or thighs to the marinade and coat them thoroughly. Allow them to marinate for at least 30 minutes, or for the best flavor, refrigerate for 2-4 hours.

Preheat your grill or grill pan over medium-high heat. If using a grill, clean the grates and oil them lightly to prevent the chicken from sticking.

Place the marinated chicken on a grill. Cook each side for 6-8 minutes, or until the internal temperature reaches 165°F (75°C). To check for doneness, use a meat thermometer.

Once cooked, take the chicken off the grill and let it rest for 5 minutes. Resting allows the liquids to redistribute, resulting in juicy, tender chicken.

Slice the chicken into strips or cubes, depending on how you want to serve it.