Preheat oven to 180ºC. Spray 12 muffin tin holes with olive oil spray.
Using a 6cm cookie cutter, cut out four circles in each sheet of pastry. Press into muffin moulds.
Divide onion, spinach, cheddar and bacon among each pastry case.
In a jug, add eggs, cream, salt and pepper. Whisk thoroughly. Divide egg mixture into each pastry case.
Bake mini quiches for 12-20 minutes. The egg filling will rise above the pastry, but when removed from the oven, they will drop. Serve hot or cold with tomato relish.