Fill a pot with plenty of water and bring to a boil. Reduce to low heat, then add the pork slices, spreading them out. Cook until the color changes, then drain in a colander and let cool.

Slice the cucumber in half lengthwise, then cut into thin diagonal slices. Remove the pits from the umeboshi and mash them with a knife to make a paste.

Combine all the ingredients in a bowl and mix well.