Fry the onion in 1 tbsp oil for about 5 minutes or until soft, add the garlic and fry for 30 seconds. Add the courgette and stir, and then add the cabbage, spinach and stock. Bring to a simmer and cook for about 3 minutes, season well.
Meanwhile, fry the bacon in a non-stick pan until it crisps up, you shouldn’t have to add any more fat. Drain on kitchen paper. You can leave the soup chunky or whizz it until smooth. Sprinkle with the bacon, if using, to serve.