For making the sushi rice, follow the package instructions.
1. Slice the cucumber as thinly as possible and sprinkle with salt. Rub the cucumber lightly and leave for 10 minutes. This will help to remove any excess water from the cucumber to keep it crisp.
2. Squeeze out any excess water from the cucumber by hand.
3. Break the smoked mackerel into small pieces.
4. Add the cucumber, smoked mackerel, pickled ginger, chives, dill and white sesame seeds to the sushi rice. Combine well to spread the ingredients evenly.
5. Serve into individual bowls or one large bowl to share. Sprinkle with the nori and drizzle over dark soy sauce to taste.