In a mixing bowl, combine the ground beef, breadcrumbs, Parmesan cheese, parsley, onion, garlic, egg, salt, pepper, and Italian seasoning. Mix until just combined; avoid overmixing.
Preheat the air fryer to 400°F (200°C) for about 5 minutes.
Form the mixture into meatballs, about 1 inch in diameter. You should have approximately 20 meatballs.
Place the meatballs in the air fryer basket in a single layer, ensuring they are not touching for even cooking.
Cook the meatballs in the air fryer at 400°F (200°C) for 10-12 minutes, or until they are cooked through and browned on the outside.
Check the internal temperature of the meatballs with a meat thermometer; it should reach 165°F (74°C).
Once cooked, remove the meatballs from the air fryer and let them rest for a few minutes. Serve with marinara sauce if desired.