Microwave or bake the potatoes until done but still firm. Plunge into a bowl of cool water until just cool enough to handle. Alternatively you can just dice the uncooked potatoes and steam in a saucepan with enough water to keep moist, until done but still firm.
Combine the beans, artichoke hearts, bell pepper, parsley, and scallions in a serving container.
Peel and dice the potatoes and add them to the bean mixture. Drizzle in the vinegar, and season with salt and pepper.
Serve at once, while the potatoes are still warm, if possible, though this is also good at room temperature.
Place each serving on a small bed of greens, and sprinkle with some seeds, if desired.