Preheat the oven to 375°F (190°C).
Cook the lasagna noodles according to package instructions. Drain and set aside.
Prepare the meat sauce: In a large skillet, heat olive oil over medium heat. Add the chopped onion and garlic, cooking until softened (about 3 minutes). Add the ground beef and cook until browned, breaking it up with a wooden spoon. Add the crushed tomatoes, tomato paste, oregano, basil, salt, and pepper. Let it simmer for 30 minutes, stirring occasionally.
Mix the ricotta cheese: In a bowl, combine ricotta cheese, egg, half of the Parmesan cheese, and fresh parsley. Stir until smooth and set aside.
Assemble the lasagna: In a 9x13-inch baking dish, start with a thin layer of meat sauce, then add a layer of noodles. Spread a portion of the ricotta mixture on top, followed by more meat sauce. Sprinkle with mozzarella and Parmesan. Repeat layers until all ingredients are used.
Bake: Cover the lasagna with aluminum foil and bake for 30 minutes. Remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and golden.
Rest the lasagna: Let the lasagna rest for 10-15 minutes before slicing and serving.
Garnish with fresh parsley before serving.