Add the beans, onion, peppers, tomatoes, garlic, water, cumin, and chili powder to a slow cooker and stir to combine.
Place the lid on the slow cooker and cook on HIGH for about 7 hours or until beans are very tender.
Puree the soup using an immersion blender, or use a stand blender and work in batches, until the soup is smooth.
Stir in 1 tsp salt then taste and season with additional salt & pepper if necessary.
Ladle the soup into bowls and serve soup topped with diced avocado and sour cream.
