Rinse the quinoa in a fine mesh sieve. Place in a pot with the water and bring to a boil. Reduce to a simmer, cover with a lid, and cook for 10-15 minutes, or until the grains are soft and translucent. A germ ring will be visible on the outside of the grains. Fluff with a fork and set aside.

Meanwhile, add the oyster sauce to the chopped chicken, toss to coat well, and let it marinate while you get the other ingredients ready.

Add some olive oil to a large saute pan and cook the onions with some salt and pepper until slightly softened. Add the chicken, and when the pieces are almost completely cooked through, add the chopped string beans and peppers. When the string beans are crisp tender, add the quinoa, stir well and cook for 1 minute more. Taste and season with salt and pepper if necessary. Garnish with chopped scallions, and serve hot or at room temperature.