Place onion into the bowl of a food processor fitted with the “S” blade; chop until very fine. Add remaining the ingredients except olive oil; process with the onion for 10 seconds.

While the machine is running, add oil in a slow, steady stream. This will help emulsify (thicken) the dressing and prevent it from separating.

Toss all the salad ingredients together in a large bowl; pour dressing over right before serving.