Preheat your air fryer to 200°C (400°F), allowing it to reach the optimal temperature for roasting.
While the air fryer heats, wash and thoroughly dry the green beans using a kitchen towel to remove excess moisture, which helps them crisp better.
Place the green beans in a large bowl, then drizzle with olive oil, tossing gently to coat all the beans evenly. This oil helps them crisp up and enhances flavor.
Add salt and pepper to taste, then give the beans another toss to distribute the seasonings evenly.
Spread the seasoned green beans in a single, even layer in the air fryer basket, making sure not to overcrowd for optimal crisping.
Roast the green beans in the air fryer for 10-12 minutes, shaking the basket gently halfway through to promote even browning and prevent sticking.
Check the green beans for doneness; they should be vibrant green with some darkened, charred spots and a crispy texture.
If desired, cook for an additional 2-3 minutes for extra crispness or more charring.
Use tongs to transfer the roasted green beans to a serving dish, then optionally squeeze fresh lemon or sprinkle with Parmesan for added flavor.
Enjoy immediately while they are crispy and smoky for the best flavor and texture.