Heat the oil in a wok or large frying pan and add the onions. Stir fry for 3 mins. add the Chinese five-spice, garlic and ginger and cook for 1 further minute.
Add the beans and stir fry over a medium heat for 5 mins.
Add the tomatoes, water and soy sauce and continue to cook for about 5-10 mins until the beans are tender and the sauce is thick.
Serve with boiled rice.