Combine cauliflower, potatoes, onion, broth, thyme, garlic powder, and ground red pepper in Crockpot® slow cooker. Cover; cook on LOW 8 hours or on HIGH 4 hours.
Pour soup into blender or food processor in batches; blend until smooth. Return puréed batches to slow cooker. Add evaporated milk, butter, salt and black pepper; stir to blend.
Top individual servings with cheese, parsley and green onions.