Add the parsley, oregano, garlic, shallot, serrano pepper, vinegar, salt, and pepper to a small bowl and stir together. Drizzle in the olive oil while stirring.
1 cup firmly packed fresh flat-leaf parsley leaves finely minced, 2 tablespoons fresh oregano leaves see note, 2 garlic cloves finely minced, 1 small shallot finely minced, 1 small serrano chili optional, 2 tablespoons red wine vinegar, 1/2 teaspoon sea salt, 1/8 teaspoon freshly ground black pepper, 1/2 cup extra virgin olive oil