Put the pumpkin and onion into a slow cooker with the lime leaves, lemongrass, ginger and soy sauce.
Cover and cook on high for 3 hours, or until the pumpkin is tender. Set aside to cool slightly. Remove the lime leaves and lemongrass stem.
Purée the mixture until smooth, using a stick blender, food processor or blender. Stir in the lime juice and sweet chilli sauce.
Ladle into bowls and drizzle with the reserved coconut cream. Serve garnished with the coriander and chilli.