Wash the fresh green beans under cold water, trim the ends, and pat them dry.
In a large mixing bowl, combine the trimmed green beans with olive oil, minced garlic, salt, black pepper, and red pepper flakes. Toss until evenly coated.
Preheat the air fryer to 400°F (200°C) for about 5 minutes.
Place the seasoned green beans in the air fryer basket in a single layer. Cook for 8-10 minutes, shaking the basket halfway through.
Once cooked, drizzle with fresh lemon juice and sprinkle with grated Parmesan cheese if desired. Serve warm.