Wash parsley and cilantro (if using) thoroughly under cold water. Pat them completely dry with paper towels to avoid a watery sauce. Destem the parsley and cilantro, discarding any thick, woody stems. Peel the garlic cloves.

In the bowl of a food processor, add the destemmed parsley, cilantro (if using), peeled garlic cloves, dried oregano, red pepper flakes, sea salt, and freshly ground black pepper. Pulse a few times until the ingredients are finely chopped but still retain some texture. Avoid over-processing into a smooth paste.

Pour in the red wine vinegar and extra virgin olive oil. Pulse again a few times until all ingredients are well combined and emulsified. The sauce should have a slightly rustic, chunky consistency. If the chimichurri appears too thick for your preference, add cold water one tablespoon at a time, pulsing after each addition, until the desired consistency is achieved.

(If not using a food processor): Finely chop the parsley and cilantro. Mince the garlic cloves very finely. In a medium mixing bowl, combine the chopped herbs, minced garlic, dried oregano, red pepper flakes, sea salt, and black pepper. Pour in the red wine vinegar and extra virgin olive oil and stir thoroughly until all ingredients are well mixed.

Taste the chimichurri and adjust the seasoning as needed. You might want more salt, pepper, red pepper flakes for extra heat, or a bit more vinegar for tang, depending on your preference.

For the best flavor, transfer the chimichurri to an airtight container, cover it, and let it rest in the refrigerator for at least 30 minutes, or ideally 2 hours, to allow the flavors to meld and deepen. Before serving, allow the sauce to come to room temperature and give it a good stir.