Preheat your oven to 425°F and line a baking sheet with parchment paper.
Spread the asparagus in a single layer on the baking sheet. Drizzle with olive oil and season with kosher salt and pepper. Toss to coat, then arrange the spears so they're not overlapping.
Roast for 12–15 minutes, until the asparagus is tender-crisp and the tips are just starting to get golden and slightly charred.
Transfer to a serving platter. Immediately scatter the lemon zest and red pepper flakes over the top.
Drizzle with a little more olive oil, then pile on generous shavings of Parmesan.
Finish with a sprinkle of flaky sea salt and serve warm.