Preheat the oven to 375°F (190°C).

Boil salted water in a large pot and cook the lasagna noodles according to package instructions.

In a large skillet, heat olive oil over medium heat. Sauté the diced onion and minced garlic until fragrant, then add the ground beef and cook until browned.

Stir in the marinara sauce and bring to a gentle simmer.

In a mixing bowl, combine ricotta cheese, egg, salt, and pepper.

Spread a thin layer of meat sauce on a greased sheet pan. Place 4 lasagna noodles on top, followed by half of the ricotta mixture, a layer of mozzarella, and more sauce.

Layer with the remaining noodles, ricotta mixture, and mozzarella. Finish with a layer of meat sauce and sprinkle Parmesan on top.

Cover with aluminum foil and bake for 30 minutes. Remove foil for the last 10 minutes to allow the cheese to bubble.

Let the lasagna cool for about 10 minutes before slicing.