In a medium bowl, combine finely chopped flat-leaf parsley, minced garlic, extra virgin olive oil, red wine vinegar, dried oregano, fine sea salt, freshly ground black pepper, and crushed red pepper flakes. Stir well and refrigerate for at least 2 hours or overnight.

Place the chicken thighs in a large bowl. Sprinkle with fine sea salt and pour half of the chimichurri sauce over the chicken. Coat thoroughly and marinate for 15 minutes at room temperature or overnight in the fridge.

Preheat your grill to medium-high heat (400°F/200°C) and lightly grease the grates with oil.

Place the marinated chicken thighs smooth-side down on the grill. Grill for 5-7 minutes until grill marks appear and the chicken releases easily. Flip and grill for another 5-7 minutes, checking for an internal temperature of 165°F (75°C).

Remove the grilled chicken from the grill and let them rest for a couple of minutes. Transfer to a platter and drizzle the remaining chimichurri sauce over the top before serving.