Mist a large frying pan with low calorie cooking spray and heat up. Throw in the onions and mushrooms, and cook until browned
Add the pepper and Worcestershire sauce and cook for a further minute
Remove the pan from the heat and add the quark. Keep stirring until it's fully incorporated
Return the sauce to the pan and stir well - it will thicken it a bit more.
Gradually raise the heat, making sure to stir the sauce till it's bubbling. Taste and check the seasoning. Add more salt and pepper to taste and then serve!