In a large skillet, heat oil over medium heat. Cook one-half of the meatballs (or as many as will fit comfortably in the skillet), turning occasionally until the outsides are browned and there is no pink remaining inside (about 6 minutes per batch of meatballs). (Tip: To test doneness, simply poke one meatball with a pointed knife and open enough to see interior). Transfer cooked meatballs to a dish and cover with aluminum foil to keep warm. Drain fat from skillet, then wipe skillet with a paper towel.
Apple Glaze
In a medium mixing bowl, combine juice, soy sauce, brown sugar, cornstarch, ginger and cayenne pepper. In the skillet you used to cook the meatballs, cook and stir sauce over medium-high heat (at a full boil) until it becomes thickened and bubbly. Cook and stir for an additional 2 minutes, then return meatballs to skillet to glaze and heat through.
Transfer meatballs and sauce to a serving dish and top with chopped green onions if desired.