To the bowl of a slow cooker, combine diced onion, oregano, cumin, chili powder, garlic powder, green chilis, broth or water, and potatoes.
Cook on HIGH for 2-3 hours, or LOW for 4-6. Stir every so often. Depending on your slow cooker, the potatoes may be tender and ready to blend earlier than the prescribed times. Check them occasionally. They should practically fall apart when poked with a fork.
When ready, use an immersion blender or carefully transfer 1-2 cup batches of soup at a time to a standard blender and puree the soup until creamy. If you moved the soup into a blender, return it to the crockpot. Stir in white beans, corn, lime juice, and cheese. Heat for an additional 10 minutes. Taste for seasonings.
To serve, ladle into bowls and top with fresh cilantro, avocado slices, and limes. Eat with tortilla chips, if you dare.