Place ingredients in a slow cooker and stir to combine. Cook for 3-4 hours on high or 8-10 hours on low. The squash pieces should be soft enough to mash easily with a fork.
Process in batches in a stand blender or directly in the slow cooker using an immersion blender until smooth and creamy.
Garnish with roasted pumpkin seeds and fresh grated parmesan cheese if desired and serve with a crusty bread.