In a large bowl, combine broccoli, bell pepper, zucchini, and red onion.
Drizzle with olive oil and toss with garlic powder, Italian seasoning, salt, black pepper, and red pepper flakes.
Arrange vegetables in a single layer in the air fryer basket. Work in batches if needed.
Air fry for 12 minutes, shaking the basket halfway through, until edges are lightly charred and vegetables are tender-crisp.
Transfer to a bowl, toss with lemon juice, and sprinkle with Parmesan before serving.
Notes
Cut all vegetables into similar sizes for even cooking. For vegan or dairy-free, omit the Parmesan. Cooking time may vary by air fryer model—start checking at 10 minutes.