Rehydrate the wakame by soaking it a bowl of cold water for about 5 minutes.
In the meantime, chop your cucumber into thin slices. In a bowl, add the rice vinegar, soy sauce and sugar, then leave to sit.
Once the wakame has rehydrated, chop it into bite sized pieces and add to a bowl with the cucumber. Mix well, serve into bowls, then garnish with a pinch of white sesame seeds.