Rinse the yams carefully and dry. Slice them thin but not too thin though. Pour 1 tablespoon avocado oil on a nonstick baking sheet and brush it all over. Cover with a layer of yams then brush them with the rest of the oil. Sprinkle za’atar, sumac and salt, and bake for 15 minutes or until the yams get golden patches. Let them cool for a few minutes before you eat.