Preheat oven to 400°F (200°C). Cut butternut squash in half lengthwise, remove seeds, and place cut-side down on a parchment-lined baking sheet.
Roast squash for 30-40 minutes until tender. Let cool slightly.
In a large pot over medium heat, sauté chopped onion and minced garlic in olive oil for about 5 minutes until fragrant.
Scoop out the flesh of the roasted squash and add it to the pot along with vegetable broth. Simmer for 10 minutes.
Puree the mixture using an immersion blender or in batches until smooth. Stir in coconut milk and adjust seasoning as needed.
Serve warm, garnished with pumpkin seeds or fresh herbs if desired.
Notes
For a smoother texture, use an immersion blender directly in the pot. If using a regular blender, puree in batches and return to the pot before adding coconut milk.