Cut mizuna into 3cm pieces, slice the shiitake mushrooms thinly, and beat the egg in a bowl. Rinse the cooked rice in a sieve under water to remove excess starch.

In a pot, combine ginger, sake, and water. Bring to a boil, then add the chicken tenders. Once it boils again, cover and simmer on low heat for 10 minutes, skimming off any foam.

Remove the chicken, let it cool slightly, and shred it into bite-sized pieces. Add the rinsed rice and shiitake mushrooms to the pot and simmer for 3–4 minutes.

Season with salt and soy sauce, then stir. Add the shredded chicken and mizuna, and cook briefly until the mizuna is tender.