1. Fire up your oven, aiming for 400 °C on your pizza stone.
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.
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.