In a mixing bowl, combine fresh orange juice, lime juice, minced garlic, olive oil, ground cumin, dried oregano, salt, black pepper, and optional red pepper flakes. Whisk together until well-blended.

Place the chicken thighs in a spacious baking dish and pour the marinade evenly over them. Coat well and refrigerate for at least 1 hour—preferably overnight.

Preheat your grill to medium-high heat (about 375°F/190°C) or your oven if you prefer baking. Ensure grill grates are clean and lightly oiled.

If grilling, place marinated chicken thighs skin-side down on the grill. Cook for about 6-8 minutes before flipping. The skin should be crispy and browned. If baking, lay thighs in a baking dish and cook for 25-30 minutes, checking for doneness.

Once cooked, let the chicken rest for 5 minutes to redistribute the juices. Garnish with fresh cilantro before serving.