Cook the noodles. Meanwhile, heat the oil in a wok or very large skillet. Sauté the onions and garlic over moderate heat until the onion is golden; about 5 minutes. Add the remaining ingredients, except the garnish, and stir-fry over moderately-high heat for about 5 minutes more, or until the sprouts and snow peas (or green beans) are tender-crisp.
When noodles are done, drain them and add them to the skillet. Continue to stir-fry for another 3 to 4 minutes. Remove from heat and serve, garnishing each serving with peanuts and cucumber dice.