heat oil in a skillet over medium-high. Add chicken, skin side down, and cook until browned, 3 to 4 minutes. Mix broth, celery, carrots, onion, thyme, and Bay leaves in a 4 to 6 quart slow cooker. Top with chicken breasts, skin side up. Cover slow cooker and cook until chicken is tender on high setting, four hours. Transfer chicken to a cutting board and allow to cool briefly.
Add noodles to the slow cooker, cover and cook until tender, 10 minutes. Remove and discard skin, fat, and bones from chicken, then shredded meat and add to soup. Season soup with salt and pepper. Garnish servings with scallions and lemon zest.