Peel, chop and boil potatoes until just soft. While potatoes are cooking, drain corn and combine with black beans (and black bean juice) and green onion. Let this heat.
When potatoes are done, mix together with the bean and corn concoction. Eat as soon as you want. It will keep for a day or two.
This is a good recipe for poor college students who need to eat cheaply and simply. And its healthy too!