1. Stir together beans, 4 cups water and salsa, if using, in slow cooker. Cover and cook on high until liquid is absorbed and beans are soft, 4 to 6 hours.
2. Season with salt. Sprinkle cheese over beans, cover and continue to cook until cheese is melted, 5 to 10 minutes. Spoon into bowls, top with additional salsa and serve with tortilla chips, if desired.