Chop the tomatoes in half and cut the cucumbers into bite-sized pieces.
Blanch the green beans: fill a medium-sized saucepan with water and bring to a boil over high heat. Add the beans and blanch for about 3 minutes. Drain in a colander and immediately run under cold water, or place in a large bowl with icy water. Cut each green bean in half.
Place the potatoes in a large pot and cover with water. Add a pinch of salt and bring to a simmer. Cook until tender, about 15-20 minutes. (You know they're done when they can be easily poked with a fork.) Drain in a colander and cut into bite-sized pieces.