Preheat your oven to 375°F (190°C).
Cook the lasagna noodles according to package instructions; drain and set aside.
In a large skillet, cook the ground beef, onion, and garlic over medium heat until the meat is browned.
Drain excess fat, then stir in marinara sauce; simmer for 10 minutes.
In a bowl, combine ricotta cheese, egg, oregano, salt, and pepper; mix well.
Spread a thin layer of meat sauce in the bottom of a 9x13-inch baking dish.
Layer 3 lasagna noodles over the sauce, followed by half of the ricotta mixture, a third of the mozzarella, and a layer of meat sauce.
Repeat the layers, finishing with noodles and remaining meat sauce on top.
Sprinkle the remaining mozzarella and Parmesan cheese over the top.
Cover with foil and bake for 25 minutes. Remove foil and bake for an additional 15 minutes until cheese is bubbly.