1. Preheat oven to 180°C/160°C fan-forced. Grease a 4cm-deep, 24cm round (base) fluted quiche dish.
2. Heat oil in a large frying pan over medium heat. Add onion. Cook, stirring, for 4 to 5 minutes or until softened. Add spinach. Cook, stirring for 1 minute or until just wilted. Remove from heat. Set aside for 5 minutes to cool.
3. Whisk eggs and half the VEGEMITE in a large bowl until combined. Whisk in flour, then milk until well combined. Stir in spinach mixture and cheese. Season with pepper.
4. Pour mixture into the prepared dish. Drop small spoonfuls of remaining VEGEMITE on top. Bake for 40 to 45 minutes or until golden and set in the middle. Stand for 10 minutes. Serve.