In a 12-inch skillet heat oil over medium-high. Add chicken; cook 6 minutes or until browned, turning once.
In a 6-qt. slow cooker combine chicken, mushrooms, chicken broth, water, leeks, celery, wild rice and salt. Cover and cook on low 6 hours or high 3 hours. Remove chicken from cooker. Coarsely shred chicken using two forks.
If using low setting, turn to high. In a blender combine the tofu, low-fat milk, flour and thyme leaves. Cover and blend until smooth. Stir into mixture in cooker. Cover and cook 30 minutes more or until thick. Stir in shredded chicken.