For sauce, stir together apple juice, vinegar, cornstarch, celery seed, and pepper. Set aside.
Spray a wok or large skillet with nonstick spray coating. Preheat over medium-high heat. Add onion and stir-fry for 2 minutes. Add cabbage and carrots; stir-fry about 2 minutes or until vegetables are crisp-tender. Remove from wok.
Add oil to hot wok, if necessary. Add ham and stir-fry 2 to 3 minutes or until heated through. Push ham from center of wok.
Stir sauce; add to center of wok. Cook and stir until thickened and bubbly. Cook and stir for 1 minute more. Return vegetables to wok. Add apple. Stir all ingredients together to coat with sauce. Cook and stir for 1 minute. Garnish with additional apple slices, if desired. Makes 4 servings.