1. **Prepare the Meat Sauce:** In a large skillet over medium heat, brown the ground beef with the chopped onion and garlic. Cook until the beef is no longer pink and the onion is softened. Drain excess fat, then add the marinara sauce, salt, and pepper. Let it simmer on low for 10-15 minutes.
2. **Prepare the Cheese Mixture:** In a bowl, mix ricotta cheese, egg, 1 cup of mozzarella cheese, Parmesan cheese, and chopped parsley until smooth.
3. **Assemble the Lasagna:** Preheat the oven to 375°F (190°C). In a 9×13 inch baking dish, spread a thin layer of meat sauce on the bottom. Place a layer of lasagna noodles over the sauce, followed by a layer of the ricotta mixture, more meat sauce, and a sprinkle of mozzarella cheese. Repeat the layers, finishing with noodles, meat sauce, and a generous topping of mozzarella cheese.
4. **Bake:** Cover the lasagna with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and golden.
5. **Garnish and Serve:** Let the lasagna cool for 10 minutes before slicing. Garnish with fresh parsley and serve.