Sauté the Garlic: Heat olive oil in a large skillet over medium heat. Add minced garlic and cook until fragrant, about 1 minute.
Brown the Beef: Add the ground beef to the skillet and cook until browned, about 5 to 7 minutes, stirring occasionally.
Add the Spinach: Stir in the chopped spinach and cook until wilted, about 2 to 3 minutes. Season with salt and pepper.
Preheat the Oven: Set your oven to 375°F (190°C).
Prepare the Baking Dish: Spread a thin layer of marinara sauce in a 9x13 inch baking dish.
Layer the Ingredients: Begin layering with 3 sheets of lasagna noodles, half of the beef and spinach mixture, half of the ricotta cheese, and a sprinkle of mozzarella cheese. Repeat this layering process.
Final Layer: For the top layer, add remaining noodles, cover with marinara sauce, and sprinkle with remaining mozzarella and Parmesan cheese.
Cover and Bake: Cover the dish with aluminum foil and bake for 30 minutes.
Uncover and Continue Baking: Remove the foil and bake for an additional 15 to 20 minutes until the cheese is bubbly and golden.
Rest Before Serving: Let the lasagna sit for 15 minutes before slicing.