Prep the ingredients: Finely chop the parsley and mince the garlic (and shallot, if using).
Combine: Add parsley, garlic, oregano, vinegar, red chile (or red pepper flakes), salt, and black pepper to a medium bowl.
Add oil: Pour in the olive oil and stir until everything is evenly mixed and the sauce looks spoonable and glossy.
Rest: Let the chimichurri sit for 15 minutes at room temperature so the flavors meld.
Serve: Stir again and serve as a sauce, dip, or marinade.
Food processor option: Add parsley, garlic, shallot, oregano, vinegar, chile, salt, and pepper to a small food processor and pulse just until chopped (do not blend into a paste). Transfer to a bowl and stir in the olive oil by hand.
