Cook the spaghetti according to the package instructions. Drain it and set aside.
Heat a skillet over medium heat and add the butter. Once melted, add the garlic and sauté until aromatic. Add the noodles and stir to combine well. Then, add the oyster sauce, Sriracha, and sugar.
Stir the noodles continuously to mix them well with the seasonings. Add the Parmesan cheese and stir to coat the noodles thoroughly. Garnish with scallions and serve immediately.
Notes
You can opt out the Sriracha and make it into regular Garlic Noodles without the heat.