Place all ingredients (except optional chive garnish) in a food processor and process until thoroughly combined, scraping down the sides as needed. Taste and adjust salt if desired (see note).
Serve immediately, alongside vegetables or whole-grain tortilla chips.
Avocado: There's actually no need to mash the avocado before processing, except that it will help you make sure you get exactly the right amount. Avocados vary in size, which could affect the ratio of the other ingredients you'd need in order to get the right flavor profile.
Salt: I typically adjust the amount of salt slightly, depending on whether I'm serving this Ranch Dip with vegetables, or with salty tortilla chips. If serving with veggies, you may like to add slightly more salt, to help the flavors pop, but since tortilla chips are salty already, you probably can get by with less salt in the dip in that case. I recommend starting with 1/2 teaspoon of salt, and tasting the dip along with your choice of dipper – then adding a little additional salt if needed.