Start by peeling and cubing the butternut squash. Peel the onion and quarter it. Peel the garlic cloves.
Add the olive oil to the slow cooker. Next, add the remaining ingredients - butternut squash, onion, garlic, vegetable broth, coconut milk, ground cumin, ground coriander, ground turmeric, salt, and black pepper. Stir until all the ingredients are well combined.
Cook in the slow cooker for 5-6 hours on low or 3-4 hours on high, until the butternut squash is tender.
Once cooked, blend everything using an immersion blender until it is smooth and creamy. Taste and adjust seasoning if needed. Serve the creamy butternut squash soup hot.
Notes
A sugar pie pumpkin or kabocha squash can be substituted for butternut squash. However, the soup will have a slightly different flavor profile.
If the butternut squash is particularly sweet, balance the flavor with lemon/lime juice or apple cider vinegar.
Adjust the consistency with extra vegetable broth or coconut milk, depending on how thick or thin you like your soup.