Combine all ingredients in a crockpot and turn to high. Cook for 4 hours. Using a slotted spoon, remove 1 cup of the beans and vegetables, and place in a blender. Add 1/2 cup of liquid from the soup and blend till smooth. Add this back into the crockpot and stir to mix in. Serve with sour cream and avocado.
Notes
Blending the beans and adding them back into the soup helps to thicken it. If you prefer it thicker, just scoop out more of the beans and vegetables and blend before adding back to the soup.