Biwaz (Parsley and Onion Salad)

Remove and discard top and root end from onion. Peel, rinse, and pat onion dry using paper towels to remove some of its sharpness. Cut onion in half lengthwise, and slice each half lengthwise into about 1/4-inch-thick slices; trim slices to measure 1 to 1 1/2 inches.

Toss onion slices in a medium bowl until all pieces are separated. Add parsley, and toss to combine. Add lemon juice, oil, sumac, and salt; toss until well combined. Serve immediately.