For a quick vegetable stock to use in this soup, place the trimmings from the vegetables and apple in a large saucepan. Add a handful of the parsley stems and cover with water. Bring to a boil, reduce to a simmer, and simmer for about 30 minutes. Strain, reserving the liquid for use as a stock and discarding the solids.
Preheat oven to 350 degrees (400 degrees if using acorn squash). Cut the squash in half and remove the seeds. Coat the squash flesh with olive oil and place the squash, cut side down (cut side up if using acorn squash), in a shallow baking pan or on a cookie sheet. Bake about 30 minutes (1 hour for acorn squash) or until soft when pricked with a fork. When cool enough to handle, scoop the flesh from the skins and put it in a bowl. Set aside. Coat a Dutch oven or soup pot with olive oil. Saute all the vegetables for the soup base until they are soft. Add the cooked squash, mixing the squash meat into the soup base vegetables. Add the chopped apple. Add 2 cups of water or stock and bring to a simmer. Pour the soup into a large bowl. Puree in batches in a blender or food processor, returning the pureed soup to the Dutch oven or soup pot set over very low heat or puree the soup in the bowl using an immersion blender. Add additional water or stock to the soup until it attains the desired consistency. Season to taste with sea salt. IMPORTANT! Always use great caution when pureeing hot liquids. If you have time, allow the soup to cool before blending. Never fill the container more than half full and cover the lid with a folded kitchen towel and hold it in place before you turn on the blender. The initial surge of the blender's contents can cause the lid to pop open, possibly scalding you if still hot and certainly making a mess of your kitchen. Reheat the soup and serve sprinkled with the chopped parsley.