Cut avocados in half. Remove pits. Scoop flesh into blender.
Add chilled broth, yogurt, water, lime juice, garlic, cilantro, green onions, cumin, salt, pepper, and cayenne.
Blend on high until completely smooth (1 to 2 minutes).
Taste. Adjust seasoning as needed.
Add water if too thick. Add avocado if too thin.
Pour into bowl or pitcher. Cover with plastic wrap.
Refrigerate at least 1 hour until very cold.
Stir well before serving.
Ladle into individual bowls.
Garnish with tomatoes, cucumber, cilantro, lime, cheese, seeds, or avocado.
Serve immediately while cold.