To the container of a blender or food processor, add the parsley, oregano, cilantro, onion, and garlic and pulse to mince. Add the red pepper flakes, olive oil, vinegar, and lemon juice and pulse 2-3 times to mix. Season with kosher salt and add more to taste. Or, finely mince all of the ingredients with a sharp knife, then whisk with the olive oil, vinegar, and lemon juice in a bowl or shake in a covered glass jar. Make ahead and store in the refrigerator 1-3 days or until ready to serve.