Position a rack in the lower third of oven and preheat oven to 250°C (230°C fan-forced). Line a large rimmed baking tray with baking paper.
On the lined tray, toss asparagus with 1 tbs oil. Arrange in 1 even row over one-half of tray. Sprinkle three-quarters of the parmesan evenly over asparagus.
Using paper towel, pat prawns dry. In a medium bowl, toss prawns with garlic, paprika, chilli flakes, if using, remaining 2 tbs oil, ¾ tsp salt and ½ tsp pepper. Spread the prawns evenly over the other side of the tray.
Roast for 10 mins or until prawns are cooked through and asparagus is tender. Sprinkle prawns with parsley. Sprinkle asparagus with remaining parmesan. Serve with lemon wedges!