In a skillet, heat olive oil over medium heat. Add beef and brown. Drain and set aside.
Place tomato sauce in saucepan. Add beef and 2 tbsp parsley and cook over medium heat for 5 minutes. Remove from heat.
In large bowl, combine ricotta, spinach, parmesan, remaining 2 tbsp parsley, oregano, nutmeg and pepper. Stir well.
Place 2 cups of tomato sauce in the bottom of a 13" x 9" baking dish. Arrange 4 lasagna noodles on top of sauce. Spread half the ricotta mixture over the lasagna and sprinkle with 1 cup of the mozzarella. Repeat the layers of sauce, noodles, ricotta, and mozzarella.
Top with the remaining 2 cups of sauce and 1 cup mozzarella, sprinkled evenly over the top
Cover the dish loosely with aluminum foil, place it on a baking sheet, and bake for 45 minutes, then remove the foil and bake an additional 20 minutes.
Remove the dish from the oven and allow it to rest for 10 to 15 minutes before serving.