While not nearly as sweet as bananas, plantains do have a sweet flavor. In this soup we keep that sweetness at bay by using firm plantains with green skins rather than riper brown-skinned ones--the sugars will have not yet developed, so the fruit will add starchy body to the soup without too much sweetness.
I've been working on this recipe for years-tweaking and fussing, and I believe it is about ready. My family and friends love it. I also use it as meat sauce filling for lasagna.