To make the dressing: in a saucepan, combine rice vinegar, sugar, kosher salt, and soy sauce. Alternatively, you can use a microwave-safe bowl and heat it in the microwave until the sugar dissolves.

Place the saucepan over medium heat and whisk the ingredients together well. Once the sugar dissolves completely, remove from the heat and let it cool. Tip: if you decrease the sugar amount (which I don't recommend), you may find that the vinegar tastes too strong. If it's still too strong for you after adding the cucumbers, you can dilute it at this stage with a very small amount of dashi (Japanese soup stock), vegan dashi, or water.

To make the sunomono

Soak dried wakame seaweed in a bowl of water and let it rehydrate for 5 minutes

Meanwhile, peel the skin of Japanese cucumbers alternately to create a striped pattern. Then, thinly slice the cucumbers into rounds.

Sprinkle 1 Tbsp Diamond Crystal kosher salt on the cucumber and gently massage it in. Set aside for 5 minutes. The salt draws out the moisture from the cucumbers so it doesn't dilute the dressing later.

Use your hand(s) to squeeze out the liquid from the rehydrated wakame seaweed and add it to a medium bowl.

Squeeze out the liquid from the cucumber slices. Add them to the bowl with the wakame.

Add sesame seeds and pour the dressing on top.

Toss to combine everything together. Serve in individual bowls or a large serving bowl.

To make the variations

Crabmeat: cut 12 pieces real or imitation crabmeat into thirds lengthwise. Add to the cucumber and wakame seaweed mixture in Step 7.
Boiled octopus: slice 6 oz octopus sashimi (boiled octopus) thinly. Add in Step 7.
Boiled salted baby anchovies: add 6 Tbsp shirasu (boiled salted baby anchovies) in Step 7.