Gather all the ingredients and pat both sides dry with a paper towel.

Combine soy sauce, brown sugar, olive oil, garlic powder, salt, pepper, and sesame oil in a large bowl. Marinate the tuna steaks for about 15 minutes, turning them occasionally.

Preheat your air fryer to a temperature of 375°F (190°C). Once the air fryer is preheated, place the tuna steaks in a single layer in the air fryer basket. Make sure there's some space between the steaks to allow for even air circulation.

Cook the tuna steaks at 375°F (190°C) for 8-10 minutes, flipping them halfway through the cooking time. The exact cooking time will depend on the thickness of the steaks and your desired level of doneness. It took me about 10 minutes for a well-done tuna steak. If you prefer medium or medium well, reduce the time accordingly.

Check the internal temperature of the tuna using a digital meat thermometer. Aim for an internal temperature of around 120-130°F (49-54°C) for rare to medium-rare. Keep in mind that tuna continues to cook slightly after being removed from the air fryer due to residual heat.

Once cooked to your preferred level, carefully remove the tuna steaks from the air fryer and let them rest for a few minutes. This allows the juices to redistribute and results in a juicier steak.