Wash the meat, dab dry and rub with salt and pepper. Place meat on the fat pan of the oven and roast in the preheated oven (electric: 200 °C/ gas: level 3) for approx. 1 1/4 hours.
Pour on some water from time to time. Wash the potatoes and cook for about 25 minutes. In the meantime, stir ketchup and sour cream until smooth. Season to taste with salt, pepper and paprika. Wash the chives, cut into fine rolls and stir into the sauce.
Halve the avocado and remove the stone. Peel the flesh, chop roughly, add lemon juice and puree. Stir in yoghurt. Season to taste with salt and pepper. Drain the potatoes, rinse them under cold water and remove the skin.
Let the potatoes cool down a little and cut them into slices. Warm up the stock, stir in mustard, vinegar and oil. Pour marinade over the potatoes and let it soak for about 15 minutes. Wash, quarter and slice the cucumber.
Wash and clean the tomatoes and cut them into small cubes. Clean, wash and cut lettuce into fine strips. Carefully mix cucumber, diced tomatoes and lettuce into the potatoes. Season again with salt and pepper.
Serve salad, meat and the sauces together. Garnish the roast crust with herb bouquets.