Wash and slice the tomatoes. Peel and halve the onion and cut into rings. Marinate tomatoes and onion with vinegar, sugar, salt, pepper and 1 teaspoon of oil. Clean, clean and halve the mushrooms.
Cut the meat loaf into thirds. Heat 1 teaspoon of oil and fry the Leberkäse for about 4 minutes while turning. Remove Leberkäse and keep warm. Fry the mushrooms in the frying fat for about 3 minutes, turning. Add cream and milk, bring to the boil and simmer for another 2 minutes.
Season to taste with salt and pepper. Wash parsley, shake dry, pluck leaves from the stalks and chop. Slice the parmesan into thin slices. Arrange tomatoes, meat loaf and mushroom cream.
Sprinkle with parsley and parmesan.