Preheat oven to 375° F.
Heat large sauté pan over medium-high heat. When hot, add oil and the onions, garlic, mushrooms, basil, oregano and red pepper flakes. Sauté for 5 minutes or until mushrooms are soft and all liquid has evaporated.
Stir in spinach and cook until it wilts. Remove pan from heat and add chicken. Season and set aside.
In a small saucepan, combine chicken broth, milk, and nutmeg. Bring to a simmer over medium heat. Once bubbling, whisk in flour and simmer until thickened, 5-10 minutes. Stir in Parmesan cheese and remove from heat.
Pour ½ cup sauce into bottom of 10×10 baking dish and top with 2 noodles, 1 cup chicken mixture, 1 cup sauce and ¼ cup mozzarella.
Repeat 3 more layers with noodles, chicken, sauce and cheese. Add remaining cheese on top.
Cover dish with foil and bake for 25 minutes. Uncover and bake for 15 minutes longer.
Let rest 5-10 minutes before serving.
