Peel and chop the pumpkin into roughly 1-inch cubes, then add it to the slow cooker along with ground cinnamon, nutmeg, and vegetable broth.
Cover and set the slow cooker to low, cooking for about 6 hours until the pumpkin is very tender and easily mashable.
Once cooked, use an immersion blender or transfer the mixture to a blender and blend until smooth and creamy, with no large chunks remaining.
Pour in the coconut milk or heavy cream, then stir well to combine, and season with salt and pepper to taste.
Return the soup to the cooker on low for a few minutes just to heat through, or serve immediately for a warm, velvety consistency.
Ladle the pumpkin soup into bowls, garnish as desired, and enjoy its comforting aroma and smooth texture.