Thoroughly whisk together all sauce ingredients in a small bowl and set aside.
Cook the spaghettini pasta according to package instructions. Drain and set aside.
In the meantime, heat ½ tablespoon oil over medium-high heat in a very large pan or heavy-bottomed pot. If you have a Wok that's great, but a large Dutch oven (or a wide frying pan) works in a pinch. Brown the chicken for 2-3 minutes, stirring a few times.
Add all the vegetables and cook for 3-4 minutes, stirring often. Pour the sauce over the vegatables and bubble up once while stirring constantly. Toss with the cooked pasta and serve with green onions and cilantro.