Place the green beans in a mixing bowl and drizzle with olive oil, tossing to coat evenly with a silicone spatula.
Sprinkle the sea salt, black pepper, garlic powder, and chili flakes over the beans, then toss again until all are evenly seasoned.
Preheat your air fryer to 200°C (390°F) for about 3 minutes, ensuring a hot environment for crisping.
Spread the seasoned green beans in a single layer inside the air fryer basket, avoiding overcrowding for maximum crispness.
Air fry the green beans at 200°C (390°F) for 8-10 minutes, shaking the basket or tossing the beans halfway through to promote even browning.
Check the beans; they should be golden around the edges and crispy when gently shaken or pressed. If not quite there, cook for an additional 1-2 minutes, watching carefully to prevent burning.
Remove the green beans from the air fryer and transfer to a serving plate. Sprinkle with lemon zest if using for a bright, fresh aroma.
Let sit for a minute to allow any residual steam to escape, then enjoy the crispy, smoky green beans immediately while they’re still crackling and hot.