Put all ingredients into a blender or food processor and puree.
Taste and add more vinegar if needed.
Put into a jar or container with lid, and let stand for 2-3 hours to allow flavours to meld.
Chimichurri sauce will keep in the fridge for up to 2 days.
Notes
You can substitute pickled jalapenos for the fresh one, just reduce the vinegar by half.If you aren't a fan of cilantro, just leave it out and sub for more parsley.