Preheat the oven to 100°C. Halve the tomatoes, cross the flesh in with a sharp knife and place the tomatoes with the section facing upwards tightly packed in a greased oven dish. Mix the Italian seasoning with the oil and spoon this over the tomatoes. Place the dish in the oven to dry the tomatoes for approx. 3 hours, leaving them a little moist. Allow to cool outside the oven, scoop them into a plastic container and store in the fridge until serving.