Slice tofu into thin strips like noodles.
Drain the oil from the tuna and set aside.
Thinly slice onion and cucumber.
Blanch the tofu noodles in boiling water, then drain well.
In a bowl, mix tofu noodles, tuna, onion, cucumber, and mayonnaise.
Season with salt and pepper to taste.
Transfer to a serving dish and sprinkle with seaweed flakes and sesame seeds.