Preheat the oven to 160°C. Chop the bacon into thin strips and dice the onion finely.
Spray a frying pan with Low Calorie Cooking Spray and, on a moderate heat, cook the bacon strips and diced onion until the bacon has coloured and the onion is soft. Set aside to cool slightly.
Place the eggs into a large bowl and whisk. Add the quark and continue to whisk until the quark is fully combined - there should be no lumps at all. Season well with salt and pepper.
Stir in half of the cheese and the bacon/onion mix. Spray a 24cm Pyrex flan dish with Low Calorie Cooking Spray and pour in the egg mixture. Make sure that there is an even distribution of bacon and onion.
Top with the remaining cheese and cook for 20 minutes until golden. If using a dish with a smaller diameter (therefore resulting in a deeper quiche) then it may need an extra 5-6 minutes in the oven.
Serve hot or cold with your choice of accompaniment.