How to Make It
Combine onion, celery, garlic, thyme, sage, and 1 tablespoon oil in a 6-quart slow cooker. Cover and cook on high until vegetables have slightly softened, about 10 minutes.
Meanwhile, heat remaining 1 tablespoon oil in a large nonstick skillet over medium-high heat. Add turkey legs; cook until well browned on all sides, about 3 minutes per side. Transfer to slow cooker; add broth, carrots, and parsnips. Reduce heat to low, cover, and cook until turkey is very tender, about 4 hours.
Remove turkey legs from slow cooker. Cut meat from bones and shred meat; discard bones. Return meat to slow cooker. Stir in kale, barley, salt, pepper, and zucchini. Cover and cook on low until barley is tender, about 1 hour. Discard thyme sprigs. Stir in lemon juice.