Chimichurri is one of most delicious and versatile sauces around. It's traditionally served with grilled steak, but it goes great with chicken and fish too. Chimichurri works well as a marinade, and is also delicious on vegetables or on grilled sausage.
Pulse the garlic and onion in the food processor until finely chopped. Add the parsley and/or cilantro, and basil, and pulse briefly, until finely chopped.
Transfer the mixture to a separate bowl. Add the Garlic Olive Oil, and vinegar, and stir. (Adding the liquids outside of the blender gives the chimichurri the correct texture. You don't want the herbs to be completely puréed, just finely chopped).
Season with salt and red pepper flakes to taste.
Store in the refrigerator until ready to serve.