In a large mixing bowl, combine the chopped spinach, ricotta cheese, 1 cup mozzarella cheese, Parmesan cheese, beaten egg, salt, and pepper. Mix well.

Set aside the spinach mixture.

In a saucepan, melt the butter over medium heat. Stir in the flour and cook for 1-2 minutes until bubbly.

Gradually whisk in the milk, garlic powder, and nutmeg. Cook until the sauce thickens, about 5-7 minutes.

Remove from heat and stir in 1 cup of mozzarella cheese until melted.

Preheat the oven to 375°F (190°C).

Spread a thin layer of white sauce on the bottom of a 9x13 inch baking dish.

Layer 3 lasagna noodles over the sauce, followed by half of the spinach mixture, and then a layer of white sauce. Repeat the layers, finishing with noodles and white sauce on top.

Sprinkle remaining mozzarella cheese on top.

Cover the baking dish with aluminum foil and bake for 25 minutes.

Remove the foil and bake for an additional 20 minutes until the top is golden and bubbly.

Allow to cool for 10 minutes before slicing and serving.