Step 1

Preheat a grill to medium high. Pierce the steak all over with a fork. Combine 3 tablespoons each ponzu sauce and wasabi mayonnaise with the vegetable oil in a large bowl. Add the steak; turn to coat. Let sit 10 minutes. Meanwhile, cook the rice as the label directs, adding the ginger to the cooking water.

Step 2

Brush the grill grates with vegetable oil. Remove the steak from the marinade; add the scallions to the marinade and set aside. Grill the steak, 8 to 10 minutes per side for medium rare. Transfer to a cutting board and let rest 5 minutes. Meanwhile, remove the scallions from the marinade and grill, turning, until charred, about 3 minutes; transfer to the cutting board.

Step 3

Fluff the rice with a fork; discard the ginger, if desired, and stir in the sesame seeds. Toss the cucumbers and carrots with the remaining 1 tablespoon ponzu sauce and the vinegar. Thinly slice the steak against the grain and roughly chop the scallions. Top each serving of rice with the cucumber-carrot mixture, steak, scallions and the remaining 1 tablespoon wasabi mayonnaise.