Toss the red onions with the coarse salt. Rub the salt into the slices and let stand for 5 minutes. Rinse the onions under cold running water and drain thoroughly. Mix with the parsley and sumac. Serve within 30 minutes.
The Slow Mediterranean Kitchen by Paula Wolfert. Copyright © 2003 by Paula Wolfert. Photographs copyright © by Christopher Hirsheimer. Published by Houghton Mifflin Harcourt. All rights reserved.