The salad holds well and can be tossed a few hours in advance--but leave out the salt until close to serving time, since it will cause the tomatoes to release their juice. Blanch the green beans up to a day ahead, and keep refrigerated.
Place the beans in a large saucepan of boiling water, and cook 3 minutes. Drain and plunge beans into ice water. Drain.
Combine beans, tomato, and remaining ingredients in a large bowl; toss well to combine.
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