Cut escalopes into thin slices. Cut onion into stripes, mushrooms into slices.
Heat oil in a pan and fry escalop stripes over high heat, spice with salt and pepper. Lift out meat and fry onions and musrooms about 5 minutes and spice with salt and pepper. Add the flour, sauteé lightly. Douse with beef stock, bring to the boil then and stirring regularly. Add meat and let all simmer over low heat about 15 minutes. Dice gherkins. Add gherkins and green pepper on the end of cooking time. Stir in cream and season to taste with salt, pepper and mustard. Garnish with parsely leaves.