Combine sauce ingredients in a bowl. Set aside.

Heat oil in a pan. Add mushrooms and sauté until deeply browned and slightly crispy. Add peppers and cook for two minutes. Pour in the sauce mixture and simmer until it becomes thick and glossy.

Toss in the scallions and noodles and coat thoroughly. Cook for another minute so the sauce clings, adding water as needed if it becomes too thick. Top with your choice of crunchy toppings, if desired. Serve hot.