Preheat the oven to 200°C/fan 180°C/gas mark 6. Halve the courgettes lengthways. Scoop out the seeds using a teaspoon and roughly chop them. Place the courgette halves on a roasting tray, brush with the oil and bake for 12-15 minutes, until just soft.
Meanwhile, add the diced chorizo to a medium saucepan over a medium heat and cook for 3-4 minutes, until golden and the oil has started to release. Add the garlic and cook for a further minute. Add the courgette seeds, tomatoes, tomato purée and dried herbs with seasoning and simmer for 5 minutes with the lid on, until the tomatoes have softened and burst slightly. Remove the lid and cook for a further 5 minutes until thickened. Stir through half the basil.
Preheat your grill to the highest setting. Divide the tomato mixture between the roasted courgettes and top with the mozzarella. Place under the grill for 3-4 minutes, until the mozzarella is melted and golden. Top with the remaining basil and divide between 4 plates to serve.