Add split peas, carrots, celery, onion, garlic, ham, broth, bay leaves, and thyme to the slow cooker. Stir to combine.
Cover and cook on LOW for 7–8 hours or HIGH for 4–5 hours, until peas are tender and the soup thickens. Stir occasionally if you’re around, but it’s not essential. Add the sweet potatoes in the last hour of cooking (or half hour on high).
Remove bay leaves, taste, and season with salt and black pepper.
Ladle into bowls, garnish as desired, and serve warm.