Cut the avocado in half, remove the pit, and scoop into a blender or food processor
Add Greek yogurt (or sour cream), cilantro, garlic, lime juice, and jalapeño (if using).
Blend until smooth and creamy.
Add water, 1 tablespoon at a time, until desired consistency is reached.
Taste and adjust salt, lime juice, or spice level as needed.
Serve immediately or store in the refrigerator.