Place all the ingredients in your food processor, starting with ½ cup water. Process until very smooth, about 1 minute, stopping once to scrape the sides of the bowl with a spatula.
Check the consistency and, if desired, add up to ¼ cup more water and process to combine.
Divide the soup among 4 individual bowls. Refrigerate, covered, for 30 minutes.
Mix again, garnish with cilantro leaves, and serve.
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Notes
I recommend using Haas avocado in this recipe. It's creamy, flavorful, and not as watery as other avocado varieties. It's OK to use regular (non-Greek) yogurt, but then you will need to add less or even no water.While you could serve the soup immediately, keeping it in the fridge for 30 minutes before serving allows the flavors to meld and dramatically improves its texture and flavor. It does taste better when it's cold. So I highly recommend that you don't skip this step.You can keep the leftovers in the fridge, in an airtight container, for 1-2 days. Remix them before serving. If the soup has thickened too much while being stored, add 1-2 tablespoons of water.