In a 3 1/2- or 4-quart slow cooker stir together squash, broth, coconut milk, onion, brown sugar, fish sauce, and Asian chili sauce.
Cover and cook on low for 4 to 5 hours or on high for 2 to 2 1/2 hours.
Use an immersion blender to carefully blend soup until completely smooth. (Or, transfer the mixture in batches to a food processor or blender; or use a potato masher to mash mixture nearly smooth.) Stir in lime juice. Ladle into bowls and top with Thai Gremolata. If desired, serve with lime wedges.
In a small bowl stir together fresh basil or cilantro, chopped peanuts, and finely shredded lime peel.