This is a rather classic Japanese small salad belonging to a large category of “Sunomono” 酢の物. When sea food is added to the salad, it is most common to use “sumino” 酢みそ as a dressing. I have posted dishes using sumiso before.
I used boiled squid, seaweed, and cucumber in this dish.
Seaweed: I soak dried “seaweed salad” (comes in a pouch with several kinds of edible seaweeds but you could use just “wakame” 若布) in water and let it rehydrate for 15 or more minutes. Squeeze out excess water and dress it with sushi vinegar and, again, squeeze out excess liquid before assembly.
Squid: I use several bodies and tentacles of very small (body is about 2-3 inch long) cleaned squid. I cook it in boiling water with salt and sake for 30 seconds to 1 minutes (Do not over cook). After removing from the water and tasting, I sprinkle on a bit of salt and sushi vinegar while it is hot and let it cool. If you salted the water enough, you may not need to salt here.
Cucumber: This is an usual treatment of cucumber; I use one mini-cucumber, sliced thinly. I lightly salt the cucumber, mix, and let it stand for several minutes. I ring out the excess water and dress it with sushi vinegar. I, again, squeeze out excess sushi vinegar before assembly.
Dressing (“Karashi sumiso” 芥子酢みそ): I use 2 tsp of sweet miso (“saikyou miso” 西京味噌), 1/3 tsp of prepared Japanse hot mustard (in a tube), 1/3 tsp of sugar, 2 tsp of rice vinegar. After checking the taste and consistency, I add either broth “dashi” or mirin to make adjustment (this time, I added very small amount of mirin).
Assembly: Squeeze out excess shushi vinegar and liquid from the cucumber and seaweed. I arragne the ingredients in three small mounds as you can see in the picture and garnish it with small wedges of skinned Campari tomato and drizzle on the dressing. I used the dressing sparingly since all the ingreidients are already seasoned. The nutty flavor of miso, sweetness and tang of hot mustard punctuated with vinegary taste are perfect in this dish. You definitely need sake for this dish, although some sparkling wines such as Proseco would also go well.