1. Preheat the oven to 375°F (190°C).
2. Cook the lasagna noodles according to package instructions if not using no-boil noodles.
3. Prepare the white sauce by melting butter in a saucepan, whisking in flour, then gradually adding milk while stirring until thickened. Season with salt, pepper, and herbs like basil and oregano.
4. In a bowl, mix cooked, shredded, or ground chicken with ricotta cheese, spinach, and optional mushrooms or other vegetables.
5. Spread a thin layer of white sauce at the bottom of a baking dish.
6. Place a layer of lasagna noodles over the sauce.
7. Spread a portion of the chicken and ricotta mixture evenly over the noodles.
8. Sprinkle a layer of mozzarella and Parmesan cheese.
9. Repeat the layers: white sauce, noodles, chicken mixture, and cheese until all ingredients are used, finishing with cheese on top.
10. Cover the dish with aluminum foil and bake for 30-40 minutes until bubbly.
11. Remove the foil and bake for an additional 10-15 minutes to brown the cheese on top.
12. Let the lasagna rest for about 10 minutes before slicing to allow it to set.
13. Serve warm with garlic bread and a fresh salad.
14. Store leftovers in the refrigerator or freeze for later use.