Preheat the oven to 375°F (190°C). Boil salted water and cook lasagna noodles until al dente. Drain and cool in cold water.
In a deep pan, heat oil and brown ground beef. Add onion, garlic, salt, pepper, and oregano; sauté. Stir in marinara sauce and simmer. Spread half a cup of sauce in the casserole dish.
In a bowl, mix ricotta, egg, parmesan, 1 ½ cups mozzarella, and parsley until smooth.
Spread cheese mixture on each noodle, add meat sauce, and roll tightly. Place seam-side down in the dish.
Spread remaining meat sauce on top and sprinkle with remaining mozzarella. Cover with foil.
Bake covered for 40 minutes, then broil for 2-3 minutes until cheese is golden.
Let cool slightly, garnish with parsley, and serve.