Bring a large pot of salted water to a boil.
Cook 8 ounces of noodles until tender, using package directions.
Reserve 1/4 cup noodle water, then drain the noodles.
Stir soy sauce, oyster sauce, brown sugar, sesame oil, fish sauce, and pepper together.
Melt 4 tablespoons butter in a large skillet over medium-low heat.
Add minced garlic and cook for 1 to 2 minutes.
Pour in the sauce mixture and let it bubble for 20 seconds.
Add the drained noodles and toss well.
Sprinkle in Parmesan and toss again.
Add noodle water, one tablespoon at a time, until glossy.
Finish with green onions, cilantro, and red pepper flakes, if wanted.
Serve hot while the noodles still look shiny.