In a 3 1/2 or 4 quart slow cooker place turkey. Sprinkle with black pepper and cayenne pepper.
In a small bowl combine chicken broth, soy sauce, ginger, lemon juice, sesame oil, and garlic. Pour over turkey in cooker.
Cover and cook on low heat setting for 5 to 6 hours or on high heat setting for 2 1/2 to 3 hours.
Remove turkey to a serving platter, reserving cooking liquid. Cover the turkey with foil to keep warm.
To prepare sauce, strain cooking liquid into a small saucepan. Combine cornstarch and water. Stir into liquid in saucepan. Cook and stir over medium heat until thickened and bubbly. Cook and stir for 2 minutes.
If desired, slice turkey. Spoon sauce over turkey. Sprinkle with green onion and sesame seeds.