For this simple chicken and Chinese long bean recipe that works well as a brown bag lunch, Mark Bittman gave loose amounts for the ingredients so that you can adjust the serving size.
Cook the long beans in boiling, salted water until crisp tender, about 2 minutes. Drain and shock in ice water; set aside. Soften a diced onion in a little oil, along with some minced garlic, for about a minute; remove. Stir fry the chicken until it turns white and is partially cooked, about 3 minutes.
Add the lemongrass, the fish sauce, coriander, chicken stock, and oyster sauce; mix well and continue cooking until the chicken is done, about 3 more minutes. Add the green beans, the onion, and garlic and toss well so that everything is coated in the sauce. Season with salt and lots of pepper and serve.