Pre-heat the oven to 190oc / gas mark 5.
Heat a medium-sized pan on medium heat and add half of the olive oil.
Gently cook the onions, carrots, and celery with a pinch of salt until soft and translucent, add the garlic and cook for another minute.
Stir in the oregano, and tomato puree, followed by the chopped tomatoes, and stock.
Leave the sauce to simmer for 15-20 minutes until the vegetables are soft and the sauce has thickened a little.
While the sauce is cooking, heat a clean pan over medium heat and add the remaining oil.
Gently fry the chorizo for 2-3 minutes until it begins to colour, then add the red peppers. Cook until the red peppers have begun to soften.
Add the blended sauce to the peppers and chorizo and bring to a gentle simmer. Then stir in the mascarpone, and penne pasta.
Stir to combine everything, then empty the pan into a large casserole dish. Cover with foil, then bake in the centre of the oven for 20 minutes.
After 20 minutes, remove the foil. And top with shredded mozzarella until it's well covered. Return to the oven for another 15 minutes until the cheese is golden and bubbling.