Bring a large pot of salted water to a boil and cook the lasagna noodles until just al dente, about 8 minutes. Drain and set aside.
In a skillet, heat olive oil over medium heat. Add chopped onions and minced garlic, sautéing until fragrant and translucent, about 5 minutes.
Add ground meat to the skillet, breaking it apart with a spoon. Cook until browned and cooked through, about 10 minutes. Season with salt and pepper.
In a mixing bowl, combine ricotta cheese with chopped spinach, nutmeg, and a splash of lemon juice or salt. Mix until smooth and well blended.
Spread a thin layer of meat sauce in the bottom of your baking dish, then layer noodles on top. Spread a layer of the ricotta mixture over the noodles, then add more meat sauce. Repeat these layers until all ingredients are used, ending with a layer of meat sauce topped with shredded mozzarella cheese.
Cover the assembled lasagna with aluminum foil and bake in a preheated oven at 180°C (350°F) for 25 minutes. Remove the foil and bake for an additional 10 minutes until bubbly and golden brown.
Let the lasagna rest for about 10 minutes to set before slicing. Garnish with chopped herbs or spooky olives for a festive touch. Serve warm and enjoy the gooey, flavorful layers!