Peel, wash and chop the potatoes. Heat the oil in a large ovenproof pan. Fry the potatoes over medium heat for about 20 minutes, turning occasionally.
Wash the pumpkin, cut in half and remove seeds. Cut the pumpkin with skin first into slices, then into cubes. Add pumpkin after 5 minutes to the potatoes. Season with salt and pepper. Add apple juice and braise everything for about 15 minutes.
Meanwhile clean and wash the rocket and drain well. Preheat the oven grill. Coarsely chop the walnuts, add them about 3 minutes before the end of the cooking time and fry them. Season again with salt and pepper.
Spread goat's cheese on the potato and pumpkin vegetables. Bake briefly under the grill until the cheese melts slightly and turns brown. Sprinkle with rocket salad and horseradish and serve immediately.