1 Rinse rosemary, shake dry, pluck needles and chop finely.
2 Rinse lemon in hot water, wipe dry and finely grate zest. Squeeze juice from lemon and reserve for serving. In a bowl, mix rosemary and lemon zest with olive oil.
3 Rinse or brush mushrooms and slice thinly. Transfer mushrooms to a baking dish and drizzle with half of the rosemary-lemon oil.
4 Season mushrooms with salt and pepper. Bake in preheated oven at 200°C (fan 180°C, gas mark 3) (approximately 400°F) until mushrooms are tender, about 10 minutes.
5 Sprinkle mushrooms with Parmesan and return to oven. Continue baking until the cheese is slightly browned, about 5 minutes.
6 Drizzle with remaining herb oil and reserved lemon juice just before serving.