Cook the quinoa according to the packaging instructions, then drain and keep warm.
Meanwhile finely slice the mushrooms and salad onions; chop the garlic and ginger. Mix the miso paste with the water and rice vinegar in a small bowl. Set aside.
Heat the vegetable oil in a wok and stir-fry garlic & ginger for 30 seconds, then add the green parts of the salad onion and cook for a minute, while stirring.
Now add the mushrooms and stir-fry for 2 minutes, then add the soy sauce and miso mixture. Let it bubble for a minute or so then mix in the quinoa and white parts of the salad onions. Add the sesame oil, stir for a few seconds to combine.
Serve with chilli flakes or fresh coriander leaves.