Season both sides of the chicken with salt & pepper
Spray a large skillet with low-calorie cooking spray.
Cook the chicken on medium heat for 3 minutes. Add a little stock to the pan if it gets too dry. Put the chicken aside.
Add a splash of beef broth to the pan and reduce heat to medium-low. Cook the onions for 5 minutes.
Add the garlic to the mixture and then add the mushrooms. Stirring occasionally, cook the mushrooms for 5 minutes.
Mix the flour with the water and continue to cook for about a minute.
Stir in the beef stock. Reduce heat to low. Add the mustard and Worcestershire sauce to the pot. Finally, add the Quark. To mix, use a balloon whisk.
Reduce heat to low and simmer the sauce for another 3 minutes.
Continue to cook the chicken for five minutes, then add it back in.
Mix chopped parsley with the sauce. Season it with salt and pepper.
Sprinkle with fresh parsley and serve over rice or pasta.