Slice your beef thinly into long strips like you'd see in stir-fry.
Mix all the marinade ingredients in a bowl. Add beef, cover and refrigerate for at least 30 mins.
While that's marinating, prepare your stir fry ingredients. Chop up into 2 inch long sticks (makes about 2-3 cups)
Mince your garlic and ginger. Slice your mushrooms thinly. Of course you can use other vegetables like red peppers. That would be tasty and add some color to the dish.
Prepare your noodles like it says on the packet but with less time because you'll be cooking it when you stir fry it. So if it tells you to boil it for 3 mins, maybe reduce that to 2 mins. After you drain the noodles. Add 2 tsp of sesame oil so they don't stick together.
Add the noodles, stir and then add the 2 tbsp oyster sauce and 1-2 tbsp soy sauce. Stir-fry for about 2 minutes until your noodles are glossy brown and hot.