In a large skillet, heat 1 tablespoon of olive oil over medium heat. Add the diced onions and cook for about 5 minutes, or until they become translucent.

Add the ground beef to the skillet and season with salt and black pepper. Cook for 7-8 minutes, breaking up the meat, until it is fully cooked.

Stir in the tomato sauce and Italian seasoning, and simmer for about 5 minutes until the sauce thickens.

In a small bowl, combine ricotta cheese, egg, and Parmesan cheese. Mix until smooth.

Spoon some of the meat sauce into the bottom of each bell pepper half. Add a layer of the ricotta mixture, then top with the remaining meat sauce.

Place the stuffed peppers in the air fryer basket. Set the air fryer to 350°F and cook for 8-12 minutes, or until the peppers are tender.

Top each stuffed pepper with shredded mozzarella cheese and return to the air fryer. Let the residual heat melt the cheese, or if needed, set the temperature to 250°F and air fry for a few more minutes.

Plate the stuffed peppers, serve, and enjoy!