Peel, pit, and roughly chop the avocado; place the avocado pieces in a food processor or blender.
Add Greek yogurt, sour cream, olive oil, lime juice, minced garlic, dried minced onion, cilantro leaves, salt, and pepper to the processor.
Process the mixture for about 10 seconds, scrape down the bowl, then process for another 10 seconds until smooth; the mixture will be thick.
With the processor running, add 1/8 cup of the water and process for 5 seconds; continue adding water slowly and pulse until the dressing reaches a pourable consistency.
Taste and adjust salt, pepper, or lime as desired, then transfer to a container and refrigerate briefly so dried minced onion softens before serving.