In a wok or saucepan, over medium heat,melt the butter.
Add the garlic and cook; stirring, until fragrant but not browned; about 2 minutes.
Add the oyster sauce, soy sauce and fish sauce; stir to combine; remove from the heat.
Meanwhile, in a 12-inch skillet or sauté pan, over high, bring 1-½ inches of water to a boil; alternatively, heat up just enough water to cover the spaghetti in a large Dutch oven or saucepan.
Add the pasta; stir a few times to make sure it’s not clumping; cook, stirring occasionally, until just shy of al dente; about 2 minutes short of the recommended cook time on the package.
Using tongs, transfer the cooked pasta to the garlic sauce, along with whatever water clings to it; reserve the pasta water in the skillet.
Increase the heat to high; add the cheese to the wok; stir with a wooden spatula or spoon and toss vigorously until the sauce is creamy and emulsified; about 30 seconds.
If the sauce looks too watery, let it keep reducing; if it looks greasy, splash some more cooking water into it and let it re-emulsify.
Stir in the scallions and serve immediately.
