Add all ingredients except bok choy, egg whites, green onion, and cilantro to the slow cooker. Cover and cook on low 6 to 8 hours, or until the vegetables are tender. Add bok choy, stir and continue cooking just until wilted, approximately 5 minutes.
In a small bowl, whisk egg whites until frothy. When the soup is hot, slowly stir while drizzling the whisked egg whites into the soup. Once all egg whites are incorporated, cook for an additional two minutes.
Ladle into bowls, and top with green onion and cilantro to serve.
Stovetop Method
Follow the same instructions above for prep, then cover and simmer until veggies are tender, approximately 2 hours. Stir every 15 minutes to prevent sticking. Add bok choy and egg whites as directed in recipe.