Add all ingredients except the flank steak to a large ziplock bag or a shallow bowl. Whisk until everything is combined, and add flank steak to the bag or pan. Flip the meat around so that it gets coated in the marinade. Refrigerate for 2 - 12 hours.
Remove the steak from the marinade and place it in the preheated air fryer basket. Cook the steak in the air fryer for about 4-6 minutes per side for medium-rare, or adjust the time to your desired level of doneness. The exact cooking time will vary depending on the thickness of the meat and your air fryer. Be sure to check the internal temperature of the steak with an instant-read meat thermometer to ensure the meat doesn't get overcooked.
Remove the steak from the air fryer and let it rest for 5 minutes before slicing. This redistributes the juices and keeps the steak nice and juicy.