In a bowl, combine parsley, cilantro, garlic, vinegar, olive oil, red pepper flakes, oregano, salt, and black pepper. Mix well.
1 cup fresh parsley, 1 cup fresh cilantro, 3 cloves garlic, 3 tablespoons red wine vinegar, ½ cup olive oil, ½ teaspoon red pepper flakes, 1 ½ teaspoons dried oregano, 1 ½ teaspoons salt, ¾ teaspoon black pepper
Pour half of the chimichurri into a small jar, cover, and refrigerate—it will be used later for serving.
Place the chicken thighs in a bowl or zip-top bag. Pour the remaining chimichurri over the chicken and toss to coat evenly. Marinate for at least 30 minutes (or up to 8 hours for deeper flavor).
1 pound skinless and boneless chicken thighs
Start preheating about 20 minutes before cooking: For charcoal grills, bank the hot coals to one side for indirect heat. For gas grills, set all burners to high and aim for 400°F (200°C).
Grill the chicken thighs for 10–15 minutes, turning occasionally, until nicely charred and the internal temperature reaches 165°F (74°C).
Transfer the chicken to a plate and let it rest for 5 minutes. Drizzle with the reserved chimichurri and serve warm.