This whole dish can be made ahead and packed up to go -- making it perfect for a picnic or potluck.
In a large pot of boiling salted water, cook green beans until crisp-tender and bright green, about 6 minutes. Drain and return to pot.
Meanwhile, in a food processor, pulse olives, parsley, anchovies, oil, and vinegar until olives are finely chopped. Add to beans and stir to combine. Season with pepper. Serve at room temperature.
Refrigerate overnight and let it come to room temperature before serving.