In a mixing bowl, combine 4 tablespoons Marukan Yuzu Ponzu with the mayonnaise and whisk until smooth. Dice the tuna into small dice, place in a mixing bowl, add the Ponzu Mayo and green onion and mix.

Cut off the bottom quarter of each nori sheet and reserve for another use. Center 1 sheet of nori on a bamboo sushi mat covered with plastic wrap. With damp hands spread a thin layer of rice onto the nori leaving a ½-inch space at the bottom, press the rice firmly down. Arrange ⅛ of the tuna mixture in a line across the rice about one third of the way down from the top of the sheet. Add one cucumber matchstick, wet the uncovered edge of the nori sheet, firmly roll the mat over the ingredients. Use the mat to help shape the roll. Sprinkle with sesame seeds and cut each roll into 8 pieces.

Serve with more Marukan Yuzu Ponzu and pickled ginger.