Prepare the vegetables as described above, then in a large saucepan, heat the oil over a medium heat.
Add the onion, pepper, courgette and celery to the pan, stir occasionally and cook until soft – roughly 8-10 minutes. Add in the garlic and mushrooms and continue to cook for a further 3-5 minutes. Add in the tomato puree, stir and cook for a couple of minutes before adding in the pasta, tinned tomatoes and a tin full of water. Season the pan, bring to a boil and simmer for 5 minutes.
Meanwhile preheat the oven to 180C fan, cube the mozzarella and grate the cheddar.
Transfer the pasta and vegetables to an oven dish, cover and bake in the oven for 15-20 minutes.
After this time, dot the mozzarella all over and sprinkle the grated cheese. Return to the oven and bake for a further 10 minutes. Check that the pasta is cooked before serving.