In a saucepan over medium heat, melt butter. Stir in flour and cook for 1-2 minutes, whisking constantly.
Gradually pour in milk, whisking to avoid lumps. Cook until thickened (about 5-7 minutes). Stir in garlic powder, onion powder, Parmesan, salt, and pepper. Remove from heat.
In a large bowl, mix shredded chicken, ricotta, 1 cup mozzarella, 1/2 cup cheddar, 1/4 cup Parmesan, basil, and oregano.
Cook lasagna noodles per package instructions. Drain and lay flat.
Preheat oven to 375°F (190°C). Grease a 9×13-inch baking dish.
Spread a thin layer of white sauce at the bottom. Add a layer of noodles, 1/3 of the chicken mixture, a handful of spinach (if using), and a drizzle of white sauce. Repeat layers, finishing with noodles and sauce.
Sprinkle the top with remaining mozzarella, cheddar, and Parmesan.
Cover with foil and bake for 25 minutes. Uncover and bake for another 10-15 minutes until cheese is golden and bubbly.
Let rest for 10 minutes before serving. Pair with garlic bread or a green salad.