To Prep
Combine the mirin seasoning and soy sauce into a small bowl with the beef slices and mix well. Allow to marinate (up to 1 hr).
To Cook
Heat a griddle pan or BBQ over a medium heat for 2 mins and sear beef for 1 min on each side. Remove and set aside.
Heat the beef broth or miso soup in a saucepan; then add the udon noodles. Loosen noodles with a fork and let noodles heat through. Stir in the oyster mushrooms and heat 2 mins.
Serve broth, udon noodles and mushrooms in a small bowl.
Top with the beef slices and serve, garnish with spring onions.
