Preheat oven to 200°C. Grease twelve 1/3-cup muffin holes.
Heat olive oil in a frying pan over medium heat. Add onion and bacon. Cook, stirring, for 3 minutes or until onion is soft. Stir in spinach. Remove from heat. Set aside for 2 minutes or until spinach wilts. Allow to cool.
Sift flour into a bowl. Combine egg, milk and extra-light oil in a jug. Mix well. Pour into flour. Stir gently until almost combined. Fold in bacon mixture and cheese. Spoon into muffin holes until three-quarters full.
Bake for 18 to 20 minutes or until a skewer inserted into the centre comes out clean. Serve warm.