Ingredients:

2 1/2 Tbsp. olive oil
1 cup chopped onion
2 Tbsp. minced garlic
8 oz. white mushrooms, thinly sliced
1 tsp. dried basil
1 tsp. dried oregano
1/2 tsp. red pepper flakes
1 1/4 tsp. kosher salt, divided
1 (6 oz.) bag fresh baby spinach
2 cups shredded cooked chicken
2 cups low-sodium chicken stock
1/4 cup all-purpose flour
2 cups whole milk
1/4 tsp. nutmeg
1/2 cup shredded Parmesan cheese
8 no-boil (oven-ready) lasagna noodles
11/4 cups shredded mozzarella cheese

Directions:

Preheat the oven to 375 degrees F (190 degrees C).
Heat a large sauté pan over medium-high heat. Add olive oil, then the onions, garlic, mushrooms, basil, oregano, red pepper flakes, and 1/4 teaspoon of salt. Sauté for 5 minutes or until the mushrooms soften, stirring occasionally.
Stir in the spinach and cook until wilted and all its moisture has evaporated.
Remove the pan from the heat and stir in the cooked chicken. Set aside. In a small bowl, make a slurry by whisking together 1/2 cup chicken stock with flour until it reaches a thick, milky consistency. Set aside.
In a small saucepan, combine the remaining 1 1/2 cups chicken stock, milk, nutmeg, and 1 teaspoon of salt. Bring to a slow simmer over medium heat, stirring occasionally. Once the mixture starts to bubble around the edges, add the slurry while whisking continuously. Simmer until thickened, about 5-8 minutes, whisking occasionally. Stir in Parmesan cheese and remove from heat. Pour 1/2 cup of the sauce into the bottom of a 10×10 inch square baking dish. Top with 2 lasagna noodles, 1 cup of the chicken mixture, 1 cup of sauce, and 1/4 cup of mozzarella, ensuring the noodles are covered with sauce. Press them down lightly if needed. Repeat the layers three more times with noodles, chicken, sauce, and cheese. The last layer should have slightly more sauce and the remaining cheese on top.
Cover the baking dish with aluminum foil and bake for 25 minutes. Uncover and bake for an additional 15 minutes. If desired, broil for 2-3 minutes to achieve a golden brown top. Let the lasagna stand for 15-20 minutes before cutting and serving.