Combine parsley, cilantro, and garlic in a food processor and pulse to chop.
Add oil, red wine vinegar, water, oregano, kosher salt, and red pepper flakes. Pulse to combine.
Cover with plastic wrap and let stand at room temperature for at least 1 hour.
Notes
To substitute dried oregano, use 2 teaspoons dried oregano and mix with ¼ cup hot water. Allow it to hydrate for 10 minutes.
This sauce can be prepared and refrigerated for up to 3 days. It is important not to use the sauce after the 3 day mark because it contains fresh garlic.
Raw garlic, which has extremely low acidity, could produce botulism (a serious toxin) when stored for too long, and that is not a risk worth taking.
Bring sauce to room temperature before serving.
Depending on taste preference, the cilantro may be omitted. Simply use more parsley in its place.