1.In a medium pot fill three quarters of the way with cold water. Peel potatoes and cut into 1 1/2 inch chunks. Add egg then turn the burner on high until water boils then reduce to medium and cook for 15-20 minutes until a fork goes into the potato smoothly. Drain water and leave potatoes in the pot. Transfer the egg.
2.Turn on the heat to medium and allow the water to evaporate. Once potatoes are dry take them off heat and mash leaving some chunks. Sprinkle 1/2 teaspoon salt, mix well then transfer to a large bowl and set aside.
3.Peel egg and mash the whole thing with a fork. Slice carrots thinly into quarters then place in a small microwave safe bowl and cover with cold water. Microwave carrots for 1 1/2 minutes then drain the water.
4.Cut cucumber into quarters then chunks. Sprinkle with 1/4 teaspoon of salt. Let sit for a few minutes until moisture comes out then squeeze the moisture out. Dice the ham into squares.
5.Add carrot, corn, cucumber, and ham to the potatoes then combine well. Add Japanese mayo, green onions, dash of salt and pepper to the bowl to taste. Add egg then mix lightly. Refrigerate for 1 hour prior to serving.