Heat a large saute pan over medium-high heat and add the oil.

Add the thinly sliced yellow onions to the pan and saute until lightly browned, approximately 10 minutes.

In a small bowl, mix the port and cornstarch to create a slurry.

Pour the port-cornstarch slurry into the saute pan with the onions and stir well to combine.

Add the chicken or turkey stock to the pan and cook over medium-high heat, stirring continuously, until the sauce thickens and becomes translucent, about 7 minutes.

Place the turkey breast in a slow cooker.

Pour the prepared sauce over the turkey in the slow cooker.

Add the dried cranberries, cinnamon stick, and thinly sliced orange to the slow cooker.

Cover the slow cooker and cook on low heat for 6 to 8 hours, or until the turkey is very tender and cooked through, and the sauce has thickened.

Serve the turkey immediately with the cranberry sauce.