In a small bowl, combine the garlic powder, onion powder, paprika, salt, pepper, rosemary, thyme, oregano, and sage. Place the beef brisket in a tray and rub with 1 tbsp of olive oil and mustard.
Sprinkle the seasoning all over and drizzle with the remaining 1 tbsp of olive oil. Gently press the rub in with your hands.
Transfer the brisket into the air fryer basket (I line mine with parchment paper for easier clean up) and cook for 35 minutes for medium - slightly pink in the middle. Cooking times will vary slightly depending on the thickness and weight of your brisket.
Transfer the brisket to a cutting board and allow it to rest for 10 minutes. Remove the string and slice thinly with an electric carving knife. Serve with roasted carrots or mashed potatoes and enjoy!
Notes
The best internal temperature will vary based on your preference, but for best results I recommend aiming for somewhere around the 195 F range when air frying.
Use a digital meat thermometer to start checking around 180 F. You want it to still be slightly pink in the middle, and also keep in mind that it will continue to cook a bit as it rests.