If you prefer to fully oven-bake the
sweet potatoes, cook for 40-50 mins,
turning them halfway through the cooking time.
Heat oven to 200C/fan 180C/gas 6. Prick
the potatoes several times with a fork, then
microwave on High for 8-10 mins, turning
once, until tender. Meanwhile, heat the oil
in a non-stick pan, add the mushrooms and
rosemary and cook over a fairly high heat,
stirring, until the mushrooms are tender and
lightly coloured. Season to taste.
Put the potatoes in the oven and roast for
15 mins until the skins start to crisp. Split
open and spoon over the mushrooms.
Sprinkle with Parmesan to serve.