Preheat oven to 350°F (175°C).
Cook lasagna noodles in salted water until al dente. Drain and rinse.
Melt butter in a saucepan. Cook onion and garlic 2 minutes.
Stir in flour and cook until lightly golden.
Whisk in chicken broth and milk. Add salt and cook until slightly thick.
Stir in 2 cups mozzarella and 1/4 cup Parmesan. Add basil, oregano, pepper.
Spread 1/3 sauce in a 9×13 baking dish.
Layer 3 noodles, ricotta, and chicken.
Add 3 noodles, 1/3 sauce, spinach, 2 cups mozzarella, and 1/2 cup Parmesan.
Add remaining noodles and remaining sauce. Sprinkle parsley and remaining Parmesan.
Bake 35–40 minutes until bubbly and golden.
Rest 10 minutes before serving.