Boil 2 cups of water in a pan over medium high heat. Add the soybean sprouts and cook for 2 minutes. Flip the sprouts over once, if cooking uncovered, for even cooking. Do not open until done if cooking covered.
Mix all the sauce ingredients in a small bowl until the sugar is dissolved.
Remove the soybean sprouts to a bowl, reserving the cooking liquid in the pan. Add 1 teaspoon of cooking oil, 1-1/2 tablespoons of the prepared sauce, and the noodles to the pan.
Cook the noodles for 6 to 7 minutes until the liquid is almost gone. When the noodles turn soft, cut with kitchen shears into shorter lengths.
Add the scallions and red pepper slices, and stir fry briefly until the vegetables are slightly wilted.
Add the soybean sprouts and the remaining sauce. Quickly toss everything until well combined before turning off the heat.