Cook and crumble bacon: Cook bacon in microwave until crisp, according to package directions. Crumble bacon.
Add vegetables and beans to slow cooker: Place potatoes, onion, carrots, beans, parsnips, celery, broth, garlic, pepper, salt, and bacon in a 5- to 6-quart slow cooker.
Cook soup: Cover and cook on LOW until potatoes and beans are tender, 5 ½ to 6 hours.
Add kale and lemon juice: Uncover and stir in kale. Cook, uncovered, until kale is tender, about 2 minutes. Stir in lemon juice.
Garnish, and serve: Ladle soup into serving bowls, and garnish with black pepper and thyme leaves.
