Either by hand, with a vegetable peeler, or a mandoline, thinly slice the cucumbers into rounds and place them in a bowl. Sprinkle with the salt, tossing to coat evenly.
Let the cucumbers sit for 10 minutes, then rinse thoroughly under cold water. Gently squeeze out excess water and set the cucumbers aside.
In the meantime, if using wakame, place it in a heatproof bowl, cover with the boiling water, and soak for 5 minutes until rehydrated. Drain, squeeze out excess water, and set aside.
In a small bowl, whisk together the white and black sesame seeds, minced garlic, rice vinegar, tamari, citrus zest, sugar, and sesame oil (if using). Add the shichimi togarashi if desired.
Combine the prepared cucumbers and rehydrated wakame (if you are using it) in a mixing bowl. Pour the dressing over the salad and toss gently to coat.
Transfer to a serving dish and, optionally, garnish with sliced scallions or furikake. Serve immediately or chill before serving.