Wash the shiitake mushrooms and vegetables thoroughly and cut them into bite-sized pieces.
Rinse the rice and put it into a pot, then add water.
Evenly spread the sliced shiitake mushrooms and vegetables over the rice.
Season with soy sauce, mirin (cooking wine), and sesame oil, adjusting to taste.
Cover the pot and bring it to a boil over high heat. Once it starts boiling, reduce to low heat and cook until done.
Once the rice is cooked, mix everything well and serve in a bowl.