Heat the sunflower oil in a flameproof casserole dish. Add the chicken and cook for about 1 minute or until the meat is just turning white. Add the onion, capsicum, garlic and ginger, and cook over medium heat, stirring often, for 5–6 minutes or until the onion is softened but not browned.
Add the carrots and water chestnuts. Pour in the stock and sherry, then heat until simmering, but not boiling rapidly. Cover and simmer for 10 minutes, stirring occasionally.
Meanwhile, mix the cornflour and sugar to a smooth paste with the soy sauce, sesame oil and lemon rind and juice. Stir the cornflour mixture into the casserole and bring to the boil, still stirring. Add the green beans, cover the casserole and simmer gently for a further 2 minutes. Stir in the bean sprouts and simmer for a final 2 minutes. Serve immediately, before the bean sprouts start to soften.