Bring a pot of lightly salted water to a boil. If the noodles are fresh, steep them in the boiling water for 1 minute, then drain. If the noodles are dry, cook according to packet directions.
In a small bowl, whisk together the stock, soy sauce and cornflour.
Heat the oil in a wok over medium-high heat. Stir in the celery, mushrooms, red capsicums and onion and cook for about 3 minutes. Add the stock mixture, beansprouts and snow peas. Continue to cook and stir for about 5 minutes, until vegetables are tender but crisp.
Stir in the cooked, drained noodles until warmed through and serve.