In a medium stock-pot over low to medium heat, add butter, onion, and spices
Saute until the onions have softened
Add all of the other ingredients (except the avocado), and bring to a boil. Reduce the heat to low and cook until the vegetables are tender.
Add the avocado, blend with an emulsion blender until creamy (blending the soup in batches in your blender will work as well)
If you prefer your soup less creamy, add more water, ¼ cup at a time, until reaching your desired consistency