In a large bowl, toss cauliflower, celery, carrot and peppers with salt. Add cold water to cover. Refrigerate, covered, overnight., Drain vegetables; rinse with cold water and drain again. In a large nonreactive bowl, whisk vinegar, garlic, oregano and pepper flakes. Gradually whisk in oil until blended. Add olives and drained vegetables; toss to coat. Refrigerate, covered, overnight to allow flavors to blend., Transfer mixture to jars. Cover and refrigerate up to 3 weeks.