Add the rice cake pieces. Boil until all the pieces float to the top. Drain them out with a sieve. Do not rinse. Mix with the prepared sauce. Set aside.
Thinly slice the beef into about 2-inch long strips. Cut stems off the mushrooms and slice into thin strips. Marinate while preparing the other ingredients.
Cut the zucchini in half lengthwise and then thinly slice crosswise and slightly diagonally to make the cuts longer. Generously sprinkle salt over zucchini slices.
In the same skillet, cook the beef and mushrooms over medium high heat until the meat is cooked through. Reduce the heat to medium low. Add the rice cakes and stir fry for another minute or two.
Add the rice cakes to the bowl with the vegetables, along with the optional ginkgo or pine nuts, and the remaining sauce. Adjust the seasoning. Serve warm.