Preheat your oven to 190°C

Lamb Sauce:

1. In a large skillet, cook the ground lamb over medium heat until browned. Drain any excess fat.
   
2. Add the Napoletana sauce, dried oregano, dried basil, dried thyme, salt, and pepper. Simmer for about 5 minutes. Set aside.
   

Spinach & Mushroom Layer:

1. In another skillet, heat olive oil over medium heat. Add minced garlic and sauté for a minute until fragrant.
   
2. If using fresh spinach, add it to the skillet and sauté until wilted. If using frozen spinach, make sure it’s thoroughly thawed, and excess water is squeezed out. Add it to the skillet and sauté briefly.
3. In a bowl, combine the cooked spinach, ricotta cheese, salt, and pepper. Mix well and set aside.

Assembly:

1. In a 23×33 cm baking dish, spread a thin layer of the lamb sauce on the bottom.
   
2. Place a layer of lasagna sheets over the sauce.
3. Spread half of the spinach and ricotta mixture over the lasagna sheets.
4. Sprinkle a third of the grated Mozzarella and Parmesan cheese over the spinach layer.
5. Repeat the layers: lamb sauce, lasagna sheets, remaining spinach mixture, and another third of the cheeses.
6. Add a final layer of lasagna sheets, top with the remaining lamb sauce, and sprinkle with the remaining cheeses.
7. Bake for 35 to 40 minutes until the cheese is melted and bubbly, and the lasagna sheets are cooked through. (note 1)
8. Allow the lasagna to rest for about 10-15 minutes after taking it out of the oven before cutting into it.
9. Garnish with fresh basil leaves or dried basil before serving.