Peel the tomatoes by blanching them in hot water, then cool and cut into 8 wedges. Chill in the refrigerator until ready to use.

Rehydrate the dried wakame in water for about 10 minutes, then squeeze out excess water. Cut into bite-sized pieces if necessary.

Thinly slice the onion vertically and soak in water to reduce sharpness. Drain well.

In a bowl, mix the toasted sesame seeds, soy sauce, vinegar, sesame oil, and pepper to make the dressing.

Add the tomatoes, wakame, and onion to the bowl with the dressing. Toss gently to combine.