Cut the king oyster mushrooms and onion into bite-sized pieces.
Briefly blanch the rice cakes in boiling water.
Heat olive oil in a pan and stir-fry the onion and king oyster mushrooms.
Add the rice cakes, gochujang, gochugaru, soy sauce, minced garlic, and water, and bring to a boil.
When the rice cakes are soft, add the green onion and stir once more.