Heat the oven to 180°C/350°F. Heat the oil over a medium heat in an oven proof pot. Add the onion and cook until soft, about 5 minutes, then add the garlic, carrots, courgette, mushroom and pepper. Cook until everything is soft, probably another 10 minutes.
Pour in the chopped tomatoes, vegetable stock, dried oregano and a good helping of salt and pepper. Bring to a simmer and cook for about 10 minutes until the sauce has thickened.
Add the spinach and stir until it has wilted into the sauce. Then add the cream cheese and allow to melt into the sauce. Add the broken lasagne sheets into the sauce, nestling them under the vegetables and making sure that all of the pasta is covered in the sauce. Top with mozzarella slices and place in the oven, uncovered, for 20 minutes.
After 20 minutes turn the heat up to 200°C/400°F and cook for another 10 minutes until the cheese has browned. Serve sprinkled with a little grated parmesan if desired.