- I recommend slicing a whole kabocha squash into cubes, roast it, and enjoy half as a side for dinner. Then sometime in the next few days, use the other half of the pre-roasted squash in this soup recipe. If you’re instead preparing this recipe with freshly cut kabocha squash, you will just need to simmer the soup in Step 2 for much longer, about 15-20 minutes, until the squash is softened.