This is a very much loved dish, and one of the most common ways of cooking vegies in olive oil. Do not shy away from using plenty of good quality olive oil in this dish. It is a great side dish, or a dish on its own when served with rice. In summer, it is often served cold, at times straight from the fridge. It can be made a day before.
Frozen green beans can be used, but fresh beans are always superior. Frozen version is quicker to prepare and cook, and also an option when green beans are out of season. One of the best green beans I recall using were straight from the garden patch of Isthmus Retreat (off Wilson's Prom, great owners, great spot).
Abla's restaurant serves also a very similar dish (see recipe in 'Lebanese Kitchen'). The recipe below is just an approximation of what I do - once you get used to this dish, no need to use a recipe. It's simple and variations in amount do not matter really (as long as there is enough olive oil, and not too many tomatoes).
One could replace onion with two garlic cloves. Add paprika or black pepper (or herbs, e.g., fresh parsley at the last minute, or dried mint). It also works if you have run out of tomatoes (or a tin of tomatoes) - just omit it, or one tablesp tomato paste could be used.
Try it also dropping some garlic yoghurt on to it before serving (mix crushed garlic with plain yoghurt, and adjust taste for salt).
1 tablesp olive oil
1 onion, diced up small
1/2 kilo green beans
2 diced tomatoes
1/3 cup additional olive oil
1 teasp salt
1 tablesp sugar
1/2 cup water
Use a medium sized pot with a lid. Gently fry the diced up onion in 1 tbsp olive oil. Once onion is soft and starts to turn colour, add the pre-washed and trimmed green beans, stirring a couple of minutes. Add tomatoes, additional olive oil, salt and sugar. Stir. Add water, cover. Cook for 30-45 minutes over low heat.
When cooked, the beans will have changed colour, turning into almost khaki green (if looking bright green still, add a tablesp of water, and continue cooking). The beans should not be crunchy, but feel soft and moist.