1Place mushrooms and zucchini in a food processor, use pulse button to finely chop. Transfer to a bowl. Repeat with onion, carrot and celery.
2Heat olive oil in a large saucepan over medium heat. Add onion, mushroom mixture, and garlic. Cook, stirring 5-8 minutes or until soft.
3Add mince, increase heat to medium-high and cook, stirring, for 5 minutes until browned all over. Add oregano and cook a further 3 minutes. Add tomato sauce and tomatoes and bring to a simmer. Season to taste. Reduce heat to low and simmer 30 minutes or until the sauce thickens.
4Cook pasta shells in a saucepan of boiling salted water following packet instructions. Drain and set aside.
5Combine pasta and sauce, mix well. Scatter with cheeseand serve.
Tip: Large pasta shells are available from delis and green grocer stores, substitute them with other pasta shapes.