If you don’t have fish sauce, or are a vegetarian, you could substitute hoisin sauce or (vegetarian) Worcestershire sauce.

1 T olive oil
1 c chopped onion
1 t minced garlic
3 c or so green beans, trimmed
3 – 4 T soy sauce, or to taste
3 T fish sauce
1/4 c water
1 medium tomato, diced
black pepper, to taste

1. Heat oil in a skillet over medium heat. Add the onion and garlic. Cook, stirring, for a few minutes, then add the green beans. Stir to coat with the oil, and saute for a couple of minutes. Add the soy sauce and fish sauce. Bring to a simmer and cook for 2 minutes, stirring occasionally. Pour in the water and let simmer until the beans are close to being done the way you like them. Add the chopped tomato and continue cooking until the beans are done and the tomato is heated through. If the mixture is too liquid, turn up the heat for a bit to evaporate most of it. Taste for seasoning and add some ground black pepper, if you like.