Spray 4 x 300 ml (½ pint) baking dishes lightly with spray oil. Heat 1 tablespoon of the olive oil in a frying pan, add the onion, garlic, sage and salt and pepper to taste and cook gently for 10 minutes until softened. Add the remaining oil, then increase the heat to high, add the mushrooms and cook, stirring, for 3–4 minutes until golden.
Add the cheese sauce and heat gently for 2–3 minutes until just bubbling.
Meanwhile, plunge the pasta into a large saucepan of lightly salted boiling water. Return to the boil and cook for 10–12 minutes or until al dente. Drain well and return to the pan.
Stir the sauce into the pasta with the parsley and season to taste with salt and pepper.
Spoon the pasta into the prepared dish and scatter over the Parmesan. Bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 15–20 minutes until bubbling and golden. Serve with a crisp green salad.