Cook bacon in a large saucepan over medium heat, stirring occasionally, until crisp, 4 to 5 minutes. Using a slotted spoon, transfer bacon to a paper towel-lined plate; set aside. Add onion to fat in pan, and cook until softened, 4 to 5 minutes. Add kale; cook until soft, 3 to 4 minutes. Add squash purée and 3 cups water (or more if necessary to achieve desired consistency); bring just to a boil. Season generously with salt and pepper. Serve garnished with reserved bacon.