Adding cucumber gives this sandwich volume and a crispy texture, enhancing the creaminess of the egg. It's tasty and so I highly recommend it!
I'm proud of this recipe, which my mother often used to make.
The key is to remove excess moisture from the cucumber. You can make this with thinly sliced sandwich bread or thicker slices. It's also tasty if you toast it lightly when it's done.
Enjoy Japanese food around the world.