Wash the meat, dab dry and dice. Clean and wash the zucchini and carrots and slice them into thin slices. Peel and finely dice the onion. Heat oil in a pan and fry the meat in two portions for about 5 minutes.
Season with salt and pepper and remove. Put the onions and vegetables into the hot frying fat, fry and deglaze with a good 1/8 litre of water. Add meat and mustard sauce, bring to the boil and braise everything for 3-5 minutes.
Season to taste with salt and pepper if necessary. Arrange on plates and serve with fresh baguette.