Cut the broccoli into bite-sized florets, keeping them roughly the same size for even cooking. Make sure the florets are completely dry.
In a large bowl, toss the broccoli with olive oil, minced garlic, salt, black pepper, and red pepper flakes until evenly coated.
Preheat the air fryer to 400°F (200°C) for 2 minutes.
Spread the broccoli in the air fryer basket in a single layer. Cook at 400°F for 7 to 9 minutes, shaking the basket halfway through, until the edges are charred and crispy.
Transfer to a serving plate, squeeze fresh lemon juice over the top, and sprinkle with grated parmesan cheese. Serve immediately.