Bring a large pot of heavily salted water to a boil over high heat. Mince the garlic, grate the Parmesan cheese, and slice the scallions if using. Place oyster sauce, fish sauce, and soy sauce in a small bowl.

Add noodles to the boiling water and cook according to package directions until tender. Meanwhile, melt butter in a frying pan and cook garlic until fragrant. Turn off heat and stir in oyster sauce mixture.

Transfer the cooked noodles to the frying pan. Add some cooking water and cook while tossing until the sauce thickens slightly. Adjust with more pasta water as needed.

Turn off the heat and add Parmesan and half of the scallions. Toss to combine and serve garnished with remaining scallions.