Rub Salt And Pepper Into The Skin Of The Chicken, And Then Place Apple And Celery Inside The Chicken. Place Chicken In Slow Cooker. Sprinkle Chopped Onion, Rosemary, And Lemon Juice And Zest Over Chicken. Pour 1 Cup Hot Water Into The Slow Cooker. Cover, And Cook On High For 1 Hour. Switch To Low, And Cook For 6 To 8 Hours, Basting Several Times.