In a small bowl, mix oyster sauce, sake, mirin, soy sauce, and sugar. Set aside the sauce.
Slice the beef to thin strips. After marinating the beef with soy sauce and sake, mix in potato starch and set aside for 10 minutes.
Take the bamboo shoots out of the can and drain. Slice the bamboo shoots to thin strips and boil for 2 minutes. Drain and set aside. Remove the seeds from the green bell peppers and slice to thin strips.
Heat a frying pan over medium heat and add in sesame oil. Stir-fry the beef from Step 2. Once the beef is cooked, add in bamboo shoots and green bell peppers. Add the sauce from Step 1 and stir everything together.
Follow the package instructions to prepare the noodles and soup.
Pour the noodles into a bowl of soup and top with the toppings from Step 4. Enjoy!