Prepare the slow cooker with nonstick cooking spray.
Place all ingredients into the slow cooker EXCEPT the cornstarch and water for thickening.
Cover and cook on low for 6 to 8 hours.
Stir together the cornstarch and water. Remove the lid and add the slurry to the slow cooker. Stir to combine.
Cover and continue cooking for 30 minutes or until the gravy is thickened.
Serve over mashed potatoes or rice.