Wash and thoroughly dry the parsley and mint - any water will dilute the sauce. Finely chop both herbs until you have about 1 cup packed parsley and 1/2 cup packed mint. Mince the garlic and shallot as finely as possible; you want them to almost melt into the sauce rather than deliver crunchy bites.

In a medium bowl, combine the chopped parsley, mint, garlic, and shallot. Add the red wine vinegar and stir to combine. Let this mixture sit for 5 minutes - the vinegar will slightly soften the raw edge of the garlic and shallot while brightening the herbs.

Whisk in the olive oil until the sauce is well combined but still slightly loose - it should look like a thin, vibrant green salsa. Stir in the oregano, red pepper flakes, salt, and black pepper. Taste and adjust: add more salt if it tastes flat, more vinegar if it needs brightness, or more red pepper for heat.

Let the chimichurri rest at room temperature for at least 10 minutes before serving, or cover and refrigerate for up to 3 days. Bring to room temperature and stir well before using - the herbs will settle and the oil may solidify slightly when cold.