Add watermelon and banana to a food processor or blender, and blend until pureed.
Puree until smooth, stopping to scrape the sides. Taste, and if you would like to add a sweetener, add coconut nectar or similar. Serve immediately, or transfer to the freezer for a firmer set gelato. Enjoy!
Recipe Note
There is normally enough natural sweetness in the watermelon and ripe banana, so sweetener is to taste.