01 - In a bowl, whisk together olive oil, lime juice, minced garlic, chili powder, cumin, smoked paprika, dried oregano, salt, black pepper, and cayenne pepper if using.
02 - Place chicken breasts or thighs in a resealable bag or shallow dish. Pour marinade over chicken, ensuring even coating. Seal or cover and refrigerate for at least 30 minutes, up to 4 hours.
03 - Preheat grill to medium-high heat in preparation for grilling.
04 - Remove chicken from marinade, discarding excess liquid. Grill chicken for 7–10 minutes per side until an internal temperature of 165°F (75°C) is reached and chicken is thoroughly cooked.
05 - Allow chicken to rest for several minutes before slicing. Garnish with chopped fresh cilantro and serve.