1 cup packed fresh parsley leaves
1/2 cup packed fresh cilantro
1/4 cup packed fresh oregano leaves
1/2 cup extra-virgin olive oil
2 tablespoons lemon juice
4 teaspoons red wine vinegar
2 cloves garlic, minced
1/2 teaspoon kosher salt
Red pepper flakes
2 pounds bone-in, skin-on chicken thighs
Place the parsley, cilantro, oregano, olive oil, lemon juice, vinegar, garlic, salt, and a pinch of red pepper flakes in a blender or food processor fitted with the blade attachment. Pulse a few times until blended but still a little chunky.
Place the chicken thighs in a large bowl. Add 1/4 cup of the chimichurri and toss to combine. Transfer the remaining chimichurri to a serving bowl.
Heat an outdoor gas grill or grill pan to medium-high heat, or heat an outdoor charcoal grill for indirect grilling. Place the chicken skin-side down on the grill (direct heat if grilling on charcoal) and cook undisturbed and uncovered until the skin is crisp and golden-brown, about 5 minutes. (Discard any leftover chimichurri marinade.) Flip the chicken and grill until the second side is browned, 4 to 5 minutes more.
Reduce the heat to medium-low or move the chicken to indirect heat if using a charcoal grill. Cover the grill (or loosely cover with foil if using a grill pan) and grill until the chicken is cooked through and registers 165°F on an instant-read thermometer in the thickest part of the meat, 15 to 20 minutes. Transfer the chicken to a serving platter and let rest for a few minutes. Serve with the remaining chimichurri sauce.