Slice half of the ginger thinly and julienne the rest.

Cut the pork belly into bite-sized pieces.

Place pork, green onion, and sliced ginger in a microwave-safe container. Add enough water to cover the ingredients. Cover loosely with plastic wrap and microwave at 600W for about 7 minutes. Rinse under running water and drain.

In another microwave-safe container, mix the seasoning ingredients (sake, salt koji, dashi powder). Add the pork and julienned ginger, then mix well. Let it marinate for 10 minutes.