Heat the oil in a large, wide pan or wok, then stir-fry the peppers for 5 mins. Add the chopped garlic and mushrooms, and cook for 5 mins more. Pour in the passata and stock, then stir in the oregano, olives and courgettes with plenty of black pepper. Leave to simmer, stirring frequently, for 10-15 mins until the vegetables are just tender and the sauce has reduced a little. Meanwhile, cook the pasta following pack instructions. To make the cheese sauce, pour the milk into a large pan and add the butter, flour, nutmeg and seasoning. Heat, stirring or whisking all the time until smooth and thickened. Stir in half the cheese and allow it to melt into the sauce. Drain the pasta and add to the tomato mixture. Pile into 2 or 3 baking dishes, pack down well, then pour over the cheese sauce (it helps to let the sauce cool and thicken a little before using so that it stays as a layer). Scatter with the remaining cheese and the bread. If eating now, bake at 200C/180C fan/ gas 6 for 40 mins until bubbling and golden. Serve with a salad.