Cook the pasta according to package instructions in unsalted water (the sauce is very salty; if using fresh noodles, don’t start cooking them until later). Cook until 1-2 minutes shy of al dente.
Meanwhile, melt the butter in a large skillet or saucepan over medium heat. Add the garlic and cook, stirring, until fragrant but not browned, about 2 minutes.
Add the oyster sauce, soy sauce, and fish and stir to combine.
Using tongs, transfer the cooked noodles to the garlic sauce. Bring over some of the starchy pasta water to help make the sauce.
Increase heat to high, add cheese and scallions, and stir and toss vigorously until the sauce is creamy and emulsified, about 30 seconds.
If sauce looks too watery, let it keep reducing. If it looks greasy, splash some more pasta water into it and let it reemulsify. Serve immediately.