Mince the onion and microwave it in a heatproof container covered with plastic wrap for 1 minute at 600W. Let it cool. Rehydrate hijiki in plenty of water, then drain.

Cut mizuna into bite-sized pieces and grate the daikon, draining excess water.

Mix milk and breadcrumbs in a bowl to moisten. Add the remaining patty ingredients and mix until sticky. Divide into two portions and shape into oval patties.

Heat vegetable oil in a frying pan over medium heat. Cook the patties until browned on one side, then flip, cover, and cook for 7–8 minutes. Remove from the pan.