Slice the cabbage, onion and mushrooms. Place to one side in a large bowl, add the diced cooked chicken, and mix well. Grate the carrots using the processor. Heat the oil in a large frying pan, add the chicken and vegetable mixture, and fry for 5 minutes, stirring continuously. Add the grated carrot and soy sauce and stir fry for further 5 minutes. Transfer to a serving dish and garnish with lemon and tomato wedges. Serve immediately.