In a large bowl, combine the diced apples, chopped onion, bread cubes, fresh sage, cinnamon, nutmeg, chicken broth, melted butter, salt, and pepper. Stir until the bread is evenly moistened.
Spread the stuffing mixture evenly across the bottom of the slow cooker insert.
Season the turkey breast on all sides with salt, pepper, and a light dusting of cinnamon.
Place the seasoned turkey breast directly on top of the stuffing layer.
Cover and cook on low for 6 to 7 hours, until the turkey reaches an internal temperature of 165°F.
Remove the turkey breast, let it rest for 10 minutes, then slice and serve alongside the apple sage stuffing.