Heat a skillet over medium heat and cook the italian sausage, breaking it apart with a wooden spoon, until browned and no longer pink. Add the diced onion and garlic and cook for 2 more minutes until softened and fragrant.
Stir in the marinara sauce, italian seasoning, salt, and black pepper. Let the sauce simmer gently for 3 to 4 minutes, then remove from heat and set aside.
In a small bowl, combine the ricotta cheese, grated parmesan, egg yolk, and fresh parsley. Stir until smooth and well blended.
Lightly grease a 6-inch round or square baking pan that fits inside your air fryer. Break the oven-ready lasagna noodles to fit the shape of the pan as needed.
Spread a thin layer of meat sauce on the bottom of the pan. Add a layer of noodle pieces, then spread half of the ricotta mixture over them, sprinkle some mozzarella, and spoon on more meat sauce.
Repeat the layers one more time, ending with the remaining meat sauce and a final generous layer of mozzarella on top. Cover the pan tightly with aluminum foil. Place it in the air fryer and cook at 350 degrees F for 20 minutes. Remove the foil and cook for an additional 5 to 7 minutes until the cheese is golden brown and bubbly.
Carefully lift the pan out of the air fryer and let the lasagna rest for at least 10 minutes before slicing. This rest is essential so the layers set properly and hold together when served.