From Paula Wolfert's Cooking of the Eastern Mediterranean - a very refreshing condiment. I did serve this last night with grilled pomegranate molasses marinated lamb and pomegranate dipping sauce [ with our unseasonabley warm weather, still able to grill from the garage ]
2 medium white onions halved and thinly sliced, salted with 1 tsp Kosher salt. Toss and let sit 5-10 min to weep and soften. Rinse, shake out or spin in a salad spinner to dry up a bit. Season with 1 tsp ground sumac or more to taste, 1/2 cup minced parsley and freshly ground black pepper. Let sit to blend flavors at least 15 min.
Lamb and salad with a warmed flatbread-pita or naan .... very nice.