Cut the onion into 5 mm half rings.
Cut the champignons in half and then cut into 5 mm slices.
Drain the water from the cooked potatoes, cool slightly. Then cut the potatoes into large pieces 1.5–2 cm in size.
Chop the garlic finely.
Heat a frying pan with vegetable oil and fry the potatoes for 5 minutes until golden brown, stirring occasionally.
Add onion to the frying pan with potatoes and stir.
Add the mushrooms, salt and pepper, stir and cook for 10 minutes.
Sprinkle the vegetables with paprika, pour wine vinegar into the pan. Mix everything thoroughly. Cover with a lid and fry for 5 minutes.
At the end of cooking, add 1 tbsp of mustard to the potatoes with mushrooms and mix. Serve the salad warm, garnished with finely chopped fresh herbs.