Combine the potato dice with just enough water to cover them in a saucepan. Bring to a slow boil, then cover and simmer until just tender but still firm. Drain and rinse under cool water until they're no longer hot. Alternatively, you can microwave or bake the potatoes in their skins until just done; then once cool enough to handle, dice them.
Combine the diced potatoes with the remaining ingredients in a serving bowl and toss together gently but thoroughly.
Serve at once or cover and refrigerate until needed.Or, if using for a picnic, pack whatever portion you need into a into a tightly lidded container to transport.