Whisk soy sauce,honey,hoisin,garlic, ginger, five-spice powder and red pepper flakes together in a small bowl.Place in a resealable plastic bag and add pork. Seal. Turn and shake to coat meat. Refrigerate overnight. Coat slow cooker bowl with nonstick cooking spray. Place pork in bowl and pour marinade over top. Cover and cook on HIGH for 4 hours or LOW for 6 hours.