Meanwhile, melt the butter in a large saucepan over medium heat.
Cook the onion and garlic in the butter until tender, stirring.
Stir in flour slowly and then salt; simmer until bubbly.
Mix in the broth and milk, and boil, stirring constantly, for 1 minute.
Stir in 2 cups of mozzarella cheese and 1/2 cup Parmesan.
Add the basil, oregano and ground black pepper.
Remove from heat and set aside.
Spread 1/3 of the sauce mixture on the bottom of the 9×13 inch baking dish.
Layer with 1/3 of the lasagna sheets, and all the ricotta and the chicken.
Arrange 1/3 of the lasagna over the chicken and layer with 1/4 of the sauce mixture, the spinach, and the remaining 2 cups of mozzarella cheese and 1/2 cup Parmesan cheese.
Arrange remaining sheets over cheese and spread remaining sauce evenly over noodles. Sprinkle with parsley and 1/4 cup Parmesan cheese.