In a medium mixing bowl, combine the lime juice, chopped cilantro, minced garlic, olive oil, cumin, smoked paprika, salt, black pepper, and red pepper flakes. Whisk together until well combined to create a marinade.
Place the chicken thighs in a resealable plastic bag or a shallow dish and pour the marinade over the chicken, ensuring all pieces are well-coated. Seal the bag or cover the dish and refrigerate for at least 1 hour, preferably overnight for maximum flavor.
Preheat your grill or oven to 400°F (200°C). If using a grill, oil the grates to prevent sticking.
Remove the chicken thighs from the marinade, shaking off any excess. If grilling, place them skin-side down on the hot grill and cook for about 6-7 minutes. Flip and grill for another 6-7 minutes until the internal temperature reaches 165°F (73.9°C).
If baking, place the chicken thighs skin-side up on a greased baking sheet and bake for 30-35 minutes or until cooked through and the skin is crispy.
Once cooked, let the chicken rest for 5 minutes before serving to allow the juices to redistribute.