In a skillet, heat olive oil over medium heat. Add minced garlic and sauté for about 30 seconds until fragrant, then add chopped spinach and stir until wilted, about 2-3 minutes.

In a medium mixing bowl, combine ricotta cheese, beaten egg, shredded chicken, and the cooled spinach-garlic mixture. Add Italian seasoning, salt, and pepper. Mix until well-combined.

In a saucepan, melt butter over medium heat. Whisk in flour, cooking for about 1 minute. Gradually add warm milk while whisking continuously. Stir for 3-5 minutes until thickened. Fold in grated Parmesan and nutmeg.

Preheat oven to 375°F (190°C). Spread 1/2 cup of creamy sauce in a baking dish. Layer lasagna noodles, half of the ricotta mixture, 1/2 cup mozzarella, and 3/4 cup sauce. Repeat the layers, finishing with noodles, remaining sauce, and leftover mozzarella.

Cover with foil and bake for 25 minutes. Remove foil and bake for an additional 15 minutes until bubbly and golden brown.

Remove from oven and let rest for 10 minutes before slicing. Serve warm.