A wonderfully versatile soup. Served as described here, it makes a refreshing appetizer or hot-weather cooler; sweetened a bit more and topped with a bit of whipped cream, it makes a delicious light dessert.
Combine all ingredients except for garnish in a blender and puree until smooth. Thicken with additional banana or yogurt; thin if desired, with more fruit juice. Chill thoroughly. Garnish each serving with a dollop of yogurt or sour cream and a fresh mint leaf, violet, or rose petal.