Prep all the ingredients - deseed the jalapeno, peel and quarter the tomatillos, and rough chop the red onion.
Make the dressing by combining all the ingredients in a food processor. Blend together, taste, adjust seasoning, then pour into an airtight jar. Serve immediately.
Notes
This salsa is best served the same day. The acid and flavor profile changes after the first day, as the combination of avocado and acid tends to become too acidic the next day.