Place parsley, garlic, red wine vinegar, dried oregano, salt, serrano pepper, and black pepper into a small food processor or blender.

Pulse for a few seconds until the herbs are finely chopped and the ingredients are well blended.

While the processor is running, slowly pour in the olive oil until the sauce reaches your preferred consistency.

Transfer the sauce to a bowl and let it rest for at least two hours to allow the flavors to meld before serving.