In a 4- to 6-qt. Dutch oven heat oil over medium. Add onion and garlic; cook 5 minutes or until onion is tender, stirring occasionally. Stir in the next six ingredients (through pepper). Cook and stir 4 minutes. Add broth. Bring to boiling; reduce heat. Simmer, covered, 20 to 25 minutes or until squash and carrot are tender, stirring occasionally. Remove from heat. Stir in coconut milk and brown sugar.
Using an immersion blender (or working in batches in a food processor or blender), blend squash mixture until smooth, adding water if needed to reach desired consistency.
Serve soup topped with yogurt, pumpkin seeds, and, if desired, additional pumpkin pie spice.
