Place all ingredients except for the lime juice and yogurt in the base of a slow cooker and cook on high for at least 4 hours.
Remove 1 ½ cups of the soup, trying to get as much of the liquid as possible and place in a blender. Puree on high until creamy, then place back in the slow-cooker.
Before serving, combine the lime juice and yogurt together. Laddle the soup into bowls and stir in the lime yogurt.
Garnish with preferred toppings. We love this with shredded cheese and crushed tortilla chips.