Preheat an air fryer to 375°F. Rub the outside of the peppers with olive oil. Set aside.
Meanwhile, heat a pan over medium heat and swirl in the remaining olive oil. Add in celery and garlic and sauté for 2 minutes.
Turn the heat up to medium-high. Add in ground beef, tomato, salt, oregano, and onion powder, and sautéuntil meat is cooked and most of the liquid evaporates, about 5-7 minutes.
Stuff pepper(s) with meat mixture. You may only need one pepper, depending on how large they are. Place into the air fryer propping the peppers up with aluminum foil balls to ensure they don’t fall over. Bake for 5-7 minutes or until slightly blistered.
Optionally garnish with basil.