Cut the green onion into 4 equal pieces.

Place dried wakame seaweed in a bowl, add plenty of water to rehydrate, then drain.

Sprinkle salt on the cod and let it sit for 5 minutes, then pat dry with a paper towel.

In a frying pan, combine water, sake, mentsuyu, and umeboshi. Heat over medium heat until boiling.

Add the cod and green onion to the pan, spoon the simmering liquid over the cod. Once the cod changes color, cover and simmer on low heat for 6 minutes.