01 - Combine parsley, oregano, garlic, shallot, olive oil, vinegar, red pepper flakes, salt, and black pepper in a bowl. Mix thoroughly and let sit for at least 10 minutes to meld flavors.
02 - Set aside 1/3 cup of the chimichurri sauce for drizzling over the cooked chicken later.
03 - Pat the chicken thighs dry with paper towels. Season both sides with 1 teaspoon of salt and 1/2 teaspoon of black pepper.
04 - Place the seasoned chicken thighs in a zip-top bag or shallow dish. Pour the remaining chimichurri over the chicken, turning to coat evenly. Marinate for at least 30 minutes, or up to 4 hours in the refrigerator.
05 - Preheat the grill to medium heat or the oven to 400°F (200°C).
06 - Remove excess marinade from the chicken to prevent burning. Grill the thighs skin-side down for 6-7 minutes per side until cooked through and juices run clear (internal temp 165°F/74°C). Alternatively, bake on a parchment-lined sheet for 25-30 minutes.
07 - Let the chicken rest for 5 minutes. Serve hot, drizzled with the reserved chimichurri sauce.