Onions peel, halve and in columns cut. Heat the fat in a pan and roast the sunflower seeds in it until golden brown. For the sauce stir yoghurt, sour cream, remaining lemon juice and walnut oil until smooth, season with salt and pepper.
Wash the herbs, chop finely and add to the salad dressing. Wash and quarter apples, remove core and stalk. Cut apples into slices. Sprinkle with the juice of 1 lemon. Arrange apples and onions in a bowl, pour sauce over them and sprinkle with sunflower seeds.
Garnish with lemon balm and parsley.