1. Preheat your oven to 375°F (190°C).
2. Cook the lasagna noodles according to package instructions. Drain and set aside.
3. In a large skillet, heat olive oil over medium heat. Add the minced garlic and sauté for about 1 minute until fragrant.
4. Add the chopped spinach, stirring occasionally, until wilted and most of the liquid has evaporated, about 5 minutes. Remove from heat.
5. In a large bowl, combine ricotta cheese, Parmesan cheese, salt, black pepper, nutmeg, and the cooked spinach. Mix until well combined.
6. Spread a thin layer of marinara sauce over the bottom of a 9×13-inch baking dish.
7. Layer 4 lasagna noodles over the sauce, followed by half of the ricotta-spinach mixture, then a third of the mozzarella cheese.
8. Repeat the layering process with another layer of noodles, the remaining ricotta-spinach mixture, and another third of the mozzarella cheese.
9. Top with the final 4 noodles, remaining marinara sauce, and the last of the mozzarella cheese.
10. Sprinkle the dried oregano over the top.
11. Cover with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 15 minutes, or until the cheese is golden and bubbling.
12. Let the lasagna rest for 10 minutes before serving, allowing the layers to set beautifully.

Remember, like my grandmother taught me, trust your senses. The aroma and the golden color of the cheese will guide you to that perfect moment of doneness.