Preheat the air fryer: Set your air fryer to 400°F (200°C) and let it heat for 3–5 minutes. A hot basket helps the steak sear instead of steam.
Prep the steak: Pat the steak cubes dry with paper towels. Moisture is the enemy of a good sear, so don’t skip this step.
Season: In a large bowl, toss the steak with oil, salt, pepper, garlic powder, onion powder, smoked paprika, and red pepper flakes if using.
Add lemon juice and soy sauce. Stir until every piece is coated.
Arrange in the basket: Spread the steak bites in a single layer with a little space between pieces. Cook in batches if needed.
Air fry: Cook for 4 minutes, shake or flip, then cook 2–4 more minutes depending on doneness. Aim for 125–130°F for medium-rare, 135–140°F for medium.
Rest: Transfer to a plate and rest 3–5 minutes.
The juices redistribute, keeping the bites tender and juicy.
Finish and serve: Toss with chopped parsley and a squeeze of lemon. Serve hot with your favorite sides.