2 ½ Tbsp olive oil, divided

1 cup chopped onion

2 Tbsp minced garlic

8 oz white mushrooms, thinly sliced

1 tsp dried basil

1 tsp dried oregano

½ tsp red pepper flakes

1 ¼ tsp kosher salt, divided

1 (6 oz) bag fresh baby spinach

2 cups shredded cooked chicken

2 cups low-sodium chicken stock

¼ cup all-purpose flour

2 cups whole milk

¼ tsp ground nutmeg

½ cup shredded Parmesan cheese

8 no-boil (oven-ready) lasagna noodles

1 ¼ cups shredded mozzarella cheese

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Preheat the oven to 375°F (190°C).
In a large skillet, heat 2 tablespoons olive oil over medium heat. Add the chopped onion and cook for 3–4 minutes until softened.
Stir in the garlic and cook for 30 seconds until fragrant.
Add mushrooms, basil, oregano, red pepper flakes, and ½ teaspoon salt. Cook until mushrooms soften and release their liquid, about 6–8 minutes.
Add spinach and cook just until wilted. Remove mixture from the pan and set aside.
In the same skillet, whisk together ½ tablespoon olive oil and flour over medium heat to form a paste. Gradually whisk in the chicken stock and milk, stirring constantly to avoid lumps.
Season with nutmeg and ¾ teaspoon salt. Simmer for about 5 minutes until slightly thickened.
Stir in Parmesan cheese until the sauce is smooth and creamy.
Spread a thin layer of sauce in the bottom of a 9×13-inch baking dish. Layer with 2 lasagna noodles, then add chicken, spinach-mushroom mixture, more sauce, and mozzarella cheese.
Repeat layers until all ingredients are used, finishing with sauce and mozzarella on top.
Cover with foil and bake for 25 minutes. Uncover and bake for another 15–20 minutes, until bubbly and golden.
Let rest for 10 minutes before slicing and serving.

Use rotisserie chicken for convenience and extra flavor.

For added richness, layer in ricotta or cottage cheese between noodles.

Ensure mushrooms and spinach are well drained to prevent excess moisture.

To make ahead, assemble up to a day in advance and refrigerate before baking.

Can be made vegetarian by omitting chicken and adding extra vegetables.