Melt butter in large skillet over medium-high heat. Add 4 slices of prosciutto and fry until crisp. Remove to paper towels to cool.
Crumble prosciutto into small pieces in Crock-Pot slow cooker. Add water, navy beans, lima beans, onion, cilantro, salt, cumin, black pepper, paprika and tomatoes with juice. Stir well to combine. Cover and cook on LOW 10 to 12 hours.
Prior to serving, fry up remaining 2 slices of prosciutto and remove to paper towels. Crumble equally on top of each bowl of stew. Serve with crispy bread.