Make the chimichurri by combining the parsley, oregano, garlic, olive oil, red wine vinegar, red pepper flakes, and salt in a bowl. Stir well and set aside to let the flavors meld.
Pat the flank steak dry. Rub with olive oil and season all over with salt, pepper, and garlic powder. Let it sit at room temperature for 15 minutes.
Preheat the air fryer to 400F. Place the steak in the basket and air fry for 6-7 minutes per side for medium-rare, or 8-9 minutes per side for medium, depending on thickness.
Transfer the steak to a cutting board and rest for 8-10 minutes - this is essential for juicy results.
Slice the flank steak against the grain into thin strips. Spoon the chimichurri generously over the sliced steak and serve.