1: Fire up your oven, aiming for 400 °C (752 °F) on your pizza stone.
You can check this quickly, accurately and from a safe distance with an infrared thermometer.
2: In a medium bowl, evenly coat the asparagus in olive oil, then gently toss with the lemon zest, garlic, Parmesan, chilli flakes, salt and pepper.
3: Place the asparagus in the cast-iron pan and evenly spread them out.
Cut the zested lemon into 4 to 6 wedges and add them to the pan.
4: Place the pan in the oven and cook the asparagus for 15 to 20 minutes, turning them every 2 to 3 minutes with tongs until the edges are slightly charred.
5: Wearing oven gloves, carefully remove the pan from the oven and place it on a wood serving board or other heat-resistant surface.
Squeeze the roasted lemons over the asparagus, serve and enjoy!