Rinse the seaweed jelly thoroughly under running water.
Blanch the seaweed jelly in boiling water for 1-2 minutes, then rinse in cold water and drain.
Julienne the cucumber and carrot into thin strips.
Prepare the sauce by mixing soy sauce, vinegar, sugar, and mustard.
Place the seaweed jelly and vegetables on a plate and drizzle with the sauce.