Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish.

In a large skillet, heat a tablespoon of olive oil over medium heat. Add minced garlic and chopped fresh rosemary, sautéing for about 1 minute until fragrant.

Add the cooked chicken and optional greens to the skillet. Stir for 2-3 minutes until the spinach wilts. Remove from heat.

In a medium saucepan, melt 4 tablespoons of butter over medium heat. Stir in the all-purpose flour to form a roux, cooking for 1-2 minutes.

Whisk in the warmed milk and chicken broth, seasoning with salt, pepper, and nutmeg. Cook until thickened, about 5-7 minutes.

Spread a thin layer of béchamel in the baking dish, layer noodles, half the chicken mixture, dollops of ricotta, and mozzarella. Repeat layers.

For the last layer, place the remaining noodles, spread the béchamel, and top with remaining mozzarella and Parmesan.

Cover with aluminum foil and bake for 30 minutes, then remove the foil and bake an additional 10-15 minutes.

Let the lasagna rest for about 10 minutes, then cut and serve warm.