Here I served hamachi zuke in a bed of baby arugula.
Marinade: This is very similar to one I use for tuna sashimi. I have made several variations of the marinade for tuna. This time, I made it a bit differently. I first put an equal amount of sake and mirin in a small sauce pan (about 3 tbs each) and let it boil so that the alcohol dissipated (no lid) and the mixture reduced to nearly half. I then added, a 1 inch square of kelp and soy sauce (2 tbs). When the mixture returned to a boil, I shut off the flame and let it cool down. Meanwhile, I dry roasted white sesame (2 tbs) in a dry frying pan until fragrant. I tipped it off into a Japanese mortar or suribachi すり鉢 and coarsely ground the sesame which I added to the marinade (leaving 1-2 tbs aside for garnish). I placed the marinade in the refrigerator to completely cool.
I sliced the hamachi sashimi rather thinly (3-5 mm) and placed the pieces in the cold marinade for 1 hour in the refrigerator. The length of marination is up to you but I marinated the pieces for beween 15 minutes to one hour.
I removed the hamachi pieces and put them in a separate bowl preserving the marinade. I mixed in chopped scallion. I placed the marinated hamachi on the greens, garnished with crumbled seasoned nori ("ajitsuke nori" 味付け海苔 from a package), the roasted white sesame seeds which were previously set aside, and a dab of wasabi. I also served the marinade on the side side just in case.