Take off the outer packaging from the turkey breast but keep the netting intact, then set it in a 6-quart slow cooker.
Season the turkey with salt and pepper, massaging them into the surface. In a separate bowl, stir together the cranberry sauce, onion soup seasoning, and orange juice. Pour this blend over the turkey.
Set the slow cooker to LOW and let it cook for 5-7 hours, until the internal temperature reads at least 165°F (75°C). In my case, it took 6 hours.
Lift the turkey out of the slow cooker and transfer it to a serving platter. Tent it with aluminum foil to retain warmth. Spoon off any visible fat from the cooking liquid, then pour the liquid into a medium-sized saucepan.
Whisk the cornstarch with the cold water in a small bowl. Heat the saucepan contents over high heat until boiling. Once boiling, pour in the cornstarch slurry while whisking continuously. Keep whisking for 1-2 minutes until the sauce thickens; lower the heat if needed to avoid scorching.
Spoon a portion of the gravy over the turkey breast before serving. Put the remaining gravy in a serving vessel and offer it on the side for those who want extra.