Blanch spinach and mung bean sprouts together in the boiling water for 5 seconds, rinse them with cold water, squeeze the water out. Set aside.
Make the vinaigrette dressing with given ingredients.
Cook noodles according to the package direction, about 6-7 minutes. Rinse with cold water and drain well. Cut the noodles if you wish. Set aside.
Heat 2 tsp oil in the skillet over medium heat and saute onion, garlic, and pepper for 1-2 minutes until they get slightly wilted. Remove the skillet from the heat. Add all the vegetables and noodles in the skillet. Pour the dressing over and toss with your hand as you gently massage everything to combine.
Serve warm or at room temperature.