Cook the pasta according to package directions. Drain and set aside.
Heat a wok or large sauté pan over medium heat. When hot, add the butter, garlic and green onion. Cook for 1 minute or until very fragrant, making sure to keep an eye on the heat so that the garlic does not burn. Add in the mushrooms and cook for 2 minutes.
Remove from heat, add in the miso, oyster sauce and stir.