1Place the onion and measured vinegar in a large, nonreactive bowl and stir to combine; set aside.
2Bring a large saucepan of heavily salted water to a boil over high heat. Add the orzo and cook, stirring occasionally, until al dente, about 8 minutes. Drain and rinse under cold water until cool. Drain well and place in the bowl with the onion-vinegar mixture.
3Add the chickpeas, celery, olives, olive oil, and herbs and toss to combine. Taste and season with salt, pepper, and additional red wine vinegar as needed. Serve at room temperature.