This full-flavored soup is remarkably low in fat and can be completed in less than an hour. Use an immersion blender, if you have one, to partially puree the soup.
Cut squash in half lengthwise. Remove the seeds and fiber, and peel. Cut into 1/2-inch pieces, and set aside.
Heat olive oil in a large stockpot over medium-low heat. Cook leek and garlic until softened, 3 to 5 minutes. Add ginger, squash, and parsnips. Stir, and cook over medium heat, 3 to 5 minutes. Add salt, pepper, and stock. Cover, and bring to a boil. Reduce to a simmer, and cook until the squash and parsnips are tender, 12 to 15 minutes. Transfer half the mixture to a food processor, and puree. Return to the stockpot until warm throughout. Adjust the seasoning to taste with salt and pepper.
Meanwhile, cut the bread into 1/2-inch cubes. Toast under the broiler until golden brown. Sprinkle with Parmesan, and return to the broiler, until the cheese begins to melt. Serve the soup in individual bowls with the toasted-cheese croutons on top.