Place the wakame pieces in a bowl of cold water and soak for a minimum of 10 minutes. Drain well in a colander, then use a salad spinner or clean tea towel to dry thoroughly.
Cut cucumbers in half lengthways, scoop out seeds with a spoon, then cut into small dice. Place in a bowl, sprinkle with salt, then cover and leave to marinate for 30 minutes in the refrigerator. Drain cucumbers and, using your hands, gently squeeze out any excess liquid.
Combine the chilled cucumber with the red onion, capsicum and tomato and combine well. Add the olive oil, apple cider vinegar and serve with freshly ground pepper.