In a 2 cup measuring cup or glass mason jar, place 2 tablespoons of the gluten free soy sauce or tamari, garlic powder, onion powder, miso paste, and brown sugar, and whisk until very smooth.
Add the remaining 4 tablespoons of tamari, sherry, rice vinegar, sesame oil, and cornstarch, and whisk to combine completely. This is the basic stir-fry sauce.
If using freeze-dried scallions, mix them in now, and set the sauce aside. If you’re making the stir fry sauce ahead of time, cover and refrigerate it for up to 1 week.
Prepare the rice noodles.
Place the thin rice noodles in a medium-size or large pot. Cover the noodles with boiling water, and swish them around a bit to begin to break up the nest, if the noodles are in a nest.
Allow the noodles to sit in the hot water, uncovered, until mostly tender (about 5 minutes). Drain the hot water, rinse the noodles with cold water and drain again.
If you’re not planning to use the noodles immediately, let them sit in cold water, covered.
Make the stir fry dish.
In a nonstick wok or large skillet over medium-high heat, place the cooking oil, the sliced onions and mushrooms. Stir the vegetables to coat them in the oil, cover the wok or skillet, and allow them to cook for 3 minutes or until beginning to soften.
Add the carrots and snow peas, stir to coat, and cover again. Allow the vegetables to cook for another 2 minutes or until the orange and green vegetables have brightened in color.
Uncover the skillet, add the prepared stir fry sauce, and stir to combine. Allow the mixture to cook, stirring infrequently, until the sauce begins to thicken (about 3 minutes).
Drain the prepared rice noodles one final time if they’re soaking in liquid, cut really long noodles in half (if you like) with kitchen shears, and add the prepared noodles to the wok or skillet. Using tongs, toss to coat the noodles completely in the sauce.
Sprinkle the dish with any fresh, chopped scallions. Divide the dish among 4 serving bowls, and serve hot.
Store leftovers in a sealed container at room temperature for up to 3 hours. Refrigerate for longer storage, and sprinkle lightly with water before reheating in a warm skillet or the microwave.