In a bowl, combine the ingredients for the marinade. Set aside 1/4 cup of the marinade to use as a dipping sauce for later, if desired.
Place the tuna steak in the sauce, cover, and marinate in the fridge for at least 20 minutes (or up to 1 hour).
When ready to make the tuna steak, start by preheating the air fryer to 380°F for 5 minutes.
Season with salt and pepper, to taste. Place the tuna steaks in a single layer. Cook for 2-3 minutes on each side, or until it reaches your desired doneness. (check with an instant thermometer.)
Carefully remove the tuna steaks from the air fryer and let rest for 1-2 minutes. Slice thinly and enjoy!