1. In a bowl, add the oyster sauce and the next 8 ingredients.
2. Cut 2 tangerines in half and squeeze the juice into the bowl.
3. Mix well and add the steak.
4. Marinate the beef for 1 hour or longer, if desired.
5. In a wok or sauté pan, heat the olive oil and melt the butter.
6. Add the beef, reserving the marinade, and sear the meat on both sides.
7. Remove from the pan and let rest for 5 minutes.
8. Thinly slice the meat and set aside.
9. In the pan, add the mushrooms and the next 3 ingredients.
10. Sauté for 3 minutes and then add the meat and the marinade to the pan.
11. Bring to a boil.
12. In a small bowl, mix together the water and the corn starch.
13. Add to the pan and mix well.
14. Sauté until the sauce thickens, about 2-3 minutes.
15. Mix in the juice from the other 2 tangerines.
16. Prepare the fresh noodles according to the package instructions.
17. To serve, place the noodles in a serving bowl, top with the beef mixture and serve.

Makes about 6-8 servings.