Prepare the flat rice noodles. Cut them into 1-cm to 2-cm wide and place them into a bowl. If using store-bought version, please check notes below on how to soften them.
Add the chile to a small bowl and top with just enough soy sauce to cover. This condiment is optional.
Using your hands, tear the mushrooms in half lengthwise. (Alternatively, you can do this with a knife.)
Heat a nonstick skillet with 1 tablespoon of oil over medium-low heat. Sauté the mushrooms until they start to form a brown crust, 3 to 5 minutes. Season with a pinch of salt and set aside the pan.
Set a fine-mesh sieve over a heatproof bowl. Line a plate with paper towels. Place the sliced shallots and the remaining 4 tablespoons of oil in a small saucepan over medium-low heat. Cook the shallots until golden brown, 10 to 12 minutes, stirring regularly with chopsticks to help separate the rings. (Lower the heat as needed along the way, so the shallots don’t darken too quickly.) Strain the shallots into the sieve, then transfer them to the towel-lined plate to cool.
To the bowl of hot oil, add the soy sauce, oyster sauce, dark soy sauce, and sugar. Whisk until the sugar has dissolved.
Place the rice noodles* in a bowl, then drizzle with the sauce and top with the mushrooms, chopped scallion, and fried shallots. Add a splash of chile oil and toss everything together. Serve with the chile in soy sauce for spooning on top.