Blend parsley, cilantro, green onion, garlic, avocado oil, red wine vinegar, lemon juice, and salt in a small food processor.* You may need to scrape the sides and pulse a few times.
2 cups parsley, 1 cup cilantro, 1 green onion, 3 garlic cloves, ½ cup avocado oil, 2 tablespoon red wine vinegar, 1 tablespoon lemon juice, 1 teaspoon salt
Combine ¾ chimichurri sauce with chicken in a large plastic bag or another container. Place chicken back in the refrigerator for 2-24 hours to marinate—Reserve the remaining ¼ sauce for topping chicken later.
2 lbs boneless skinless chicken thighs
Preheat the oven to 375F. Do not cook chicken until the oven is almost preheated, or you may end up with chicken ready for the oven before the oven is ready for the chicken.
Place an oven-safe skillet such as a cast iron skillet over medium heat. When the skillet is hot, add chicken top side down first. (So the side that is pretty and smooth, put that DOWN first.) Make sure to pour all that good marinade into the skillet too!
Once the chicken has a nice golden brown sear to it, you can flip all the pieces of chicken over.
Place the entire skillet in the oven for 15-20 minutes or until the chicken reaches an internal temperature of 165F. Time will vary by the thickness of the chicken thighs.
Top with more chimichurri sauce right before serving.