Soak the wakame for at least 30 minutes. Then for 10 minutes, exchange the water and rinse the seaweed at least 3 - 4 times. Frozen wakame is very salty so make sure you get most of it off or it will affect the taste. Move the wakame to a colander to drain as you prepare the other vegetables.
Thinly slice the carrot,onion, and cucumber into long strips. Chop the tomato into chunks (about ½ in cubes). Roughly chop the seaweed into bite-sized pieces as it comes in very long strips. Add everything into a mixing bowl.
Add vinegar, salt, and sugar/sweetener, and hondashi. Mix. Taste and add more vinegar, salt, and sugar/sweetener as needed.