Pre-heat 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.
Stir in half of the cheese and the bacon/onion mix. Spray a 24cm 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.
Serve hot or cold with your choice of accompaniment.