This type of side dish belongs to a general category of "sunomon" 酢の物 or "vinegard items". This is my version of wakame salad. Mark's Izakaya Cookbook has two entries of this kind;
VINEGARD WAKAME SALAD わかめ酢 (P16)
NANOHANA RABE AND WAKAME SEAWEED SALAD 菜の花とわかめのサラダ (P112)
You can make many variations by changing the dressing and/or adding (or removing) any ingredients available (or not available) at a given time. But you need to use vinegar dressing to qualify for "sunomono". The closest we can get for nanohana here in the U.S. is brocolli rabe (rapini) but it is too bitter and too tough to eat raw. For this dish, I blanched the broccoli rabe. For cucumber, in stead of Japanese cucumber, I used American "mini cucues" which became available in our grocery store recently. It is closest to Japanese cucumber in size and taste (of course, you could get a Japanese cucumber from a Japanese grocery store). I also added skinned tomato (we do not like tomato skin), avocado, and wakame. I cut the cucumber in "jabara" 蛇腹 or "snake belly" fashion as suggested in Mark's book. If you have not seen how this is done, please check out this youtube episode. For dressing, I used "ponzu" (ポン酢) here (Mark's book has a recipe p154 but good quality one can be bought in a bottle) but you can make "nihaizu" 二杯酢 (rice vinegar, soy sauce and dashi) or "sanbaizu" 三杯酢 ("nihaizu" plus mirin) or simply use "sushi vinegar" (this is not just rice vinegar but seasoned with sugar and salt) from the bottle. We usually omit "dashi" since the liquid from the vegetables takes out some of the harshness of the vinegar. Other common variations of the dressings, especially if you add seafood such as boiled squid legs, octopus, or shrimp, are "sumiso" 酢みそ (Miso paste, sugar and rice vinegar) and "karashi sumiso" ("sumiso" plus Japanese hot mustard).