Step 1Combine the rice vinegar and the sugar in a small bowl. Stir in the pickled ginger. Let them stand for the flavors to mingle, 5 minutes.
Step 2Combine the cilantro, onions, salt and sesame oil in a small bowl.
Step 3Cut the drained tofu crosswise into 6 slices. Put 1 slice of tofu on a serving plate. Cut the slice in half lengthwise, then crosswise into sixths, forming cubes. Spoon about 1 tablespoon of the onion mixture over the top of the cubes, smoothing it so all are covered. Repeat with the remaining tofu. Serve with the pickled ginger vinegar on the side.