Wash green beans and trim stem ends. Pat completely dry with a paper towel — surface moisture causes steaming instead of blistering in the air fryer.
Add dry beans to a large bowl. Drizzle with olive oil and toss to coat evenly. Add garlic, salt, pepper, onion powder, and smoked paprika. Toss again until every bean is well coated.
Preheat air fryer to 375°F for 3 minutes before adding the beans.
Add seasoned beans to the basket in a single layer — do not overcrowd. Cook in batches if needed. Air fry at 375°F for 8–10 minutes, shaking the basket halfway through. Check at 8 minutes — beans should be tender with slightly blistered edges.
Transfer to a plate immediately. Add a squeeze of lemon juice, grated parmesan, or red pepper flakes. Serve right away.