Marinate and cook the soy chop: Drain the rehydrated soy slices and squeeze out any excess water. In a small bowl, combine the soy sauces, sugar, and hot water, stirring until the sugar dissolves. Add the soy slices and toss to coat them in the sauce, gently squeezing the slices to help them absorb the marinade. Sprinkle with the cornstarch and toss to evenly coat the soy slices.
Heat the oil in a large wok or nonstick pan over medium heat. Pan-fry the marinated soy slices in a single layer, flipping them to sear both sides until golden brown, 5 to 8 minutes. Transfer the soy slices to a bowl and set aside.
Char the noodles: In the same wok, heat the oil over medium-high. Add the fresh rice noodles, spreading them in a single layer in the pan. Allow the noodles to sear on one side, undisturbed, for about 1 minute. Flip the noodles and continue cooking until both sides develop char marks, about 2 more minutes.
Spread the mung bean sprouts over the noodles. Drizzle with the soy sauces, then season with the mushroom seasoning. Turn the heat to high and toss the noodles until they are evenly coated with the sauce and the bean sprouts are wilted, about 1 minute more.
Serve: Add the pan-fried soy slices back to the wok, then fold in the scallions and cook until the scallions are slightly wilted. Remove from the heat and serve the dish warm.