Drain the pineapple on a sieve. Peel onions and cut them into rings. Heat oil in a large pan. Fry the meatloaf in it for about 5 minutes. In the meantime boil up 1/2 litre of salted water for the puree.
Remove the pot from the heat. Pour in the milk. Stir in the puree flakes briefly, allow to swell for about 1 minute and stir again with a wooden spoon. Remove Leberkäse from the pan and keep warm. Fry the onion and pineapple rings in the frying fat until golden brown.
Season with salt and pepper. Wash parsley and chop finely, except for a few leaves for garnishing. Arrange Leberkäse, pineapple, onions and mashed potatoes on plates. Sprinkle with parsley and garnish.