CHIMICHURRI SAUCE: Place all ingredients into a food processor; cover and process until parsley and cilantro is coarsely chopped.
POTATO SALAD: Boil potatoes in lightly salted water until tender, about 8-10 minutes. Drain well. Place potatoes into a large bowl and refrigerate for 1 hour.
Just before serving, add celery and red bell pepper to the potatoes. Gently toss with a 1/2 cup chimichurri sauce. Serve potato salad alongside your favorite barbecue.