Japanese Potato Salad

Place potatoes in a large pot and add enough cold water to cover by 1 inch. Season generously with salt, set over high heat, and bring to a boil. Reduce to a simmer and cook until potatoes are easily pierced with a fork, 10 to 15 minutes. Drain potatoes and transfer to a large bowl. Let cool.

While potatoes are cooking, place cucumbers in a bowl and sprinkle 1/2 teaspoon salt. Mix well, then let stand for 10 minutes. Drain any accumulated water, then gently squeeze cucumbers to remove excess liquid. 

In a small bowl, stir together rice vinegar, mayonnaise, and hot mustard until well mixed.

Mash potatoes with a masher or a large fork, allowing some small lumps to remain. Add cucumbers, carrots, onions, eggs, green onions, and mayonnaise mixture. Mix well and season with salt. The salad can be refrigerated up to 1 day.