- Preheat the oven to 200 degC.
- Heat the oil in a large frying pan and cook the sliced onions until softened.
- Add the mince and cook until browned all over. Pour over the beans and tomatoes and simmer for 20 minutes.
- Cook pasta shells in boiling water according to the packet instructions, then drain and add to the sauce.
- Mix well, then spoon into a large ovenproof dish, scatter with grated cheese and bake for about 15 minutes.
- Serve immediately, with a side salad.