Italian Sausage-Summer Squash Soup

I like the mix of half sweet and half spicy sausage, but use all of one kind if you prefer. It may be easier to find the raw sausage in links that you can cut open and cook. If the sausage is extremely lean, you may need to add 1 tablespoon more olive oil to help it cook with the vegetables. Vegetarians can use meat-substitute crumbles, but the flavor may be too bland, so add extra Italian seasoning.