Spray slow cooker with nonstick cooking spray. Place turkey breast in slow cooker, bottom meatier side up. Squeeze one half of the lemon over the breast. Then sprinkle with lemon pepper and poultry seasoning. Place both lemon halves under the turkey breast.
Cover with lid and cook on low for 5-7 hours. Remove turkey and let rest for 15 minutes before cutting and serving.
While turkey rests, pour liquid from slow cooker into small bowl, removing lemons and skimming off any fat. In a saucepan, combine chicken broth and cornstarch, stirring until smooth. Add cooking liquid, bring to a boil and cook for 2 minutes. Pour over turkey and serve.