Sprinkle onions neatly with salt and knead well with your hands, then let stand for about 15 minutes. Then rinse the onions with cold water and drain, pat dry with kitchen paper. Mix in the parsley and sumac. Put aside.
Roll the liver in flour and in portions in hot! Fry the oil until brown. Degrease on kitchen paper. Season to taste with the spices and keep warm until serving.
Arrange with the onions and tomato slices on a large platter, serve with white bread. Can be eaten warm or chilled!