Chicken and Mushroom White Lasagna

Preheat the oven to 375º. Make filling: Place thawed spinach in a fine-mesh strainer, and press down with a rubber spatula until all almost completely dry. Move spinach to a clean tea towel or layered paper towels, and wring all excess moisture from the spinach until completely dry. In a large nonstick skillet, heat 1 tablespoon of olive oil over medium high heat. Add the mushrooms, tossing in the oil to coat. Cook, stirring occasionally, until starting to turn golden brown, about 5 minutes. Add 1 tablespoon of olive oil, and add the onions, ½ tsp of salt, and a few grinds of black pepper. Cook, tossing with the mushrooms, until the onions begin to soften, about 3 minutes. Add ½ tablespoon of olive oil and garlic, and cook for 1 minute. Add the drained spinach and 1 teaspoon of salt, and stir until the spinach is heated through. Remove from heat and set aside to cool.  In a separate bowl combine the ricotta, egg, 1 tablespoon of oregano, 1 tablespoon of rosemary, parsley, salt, and a few grinds of fresh black pepper. Make the Mornay sauce: In a medium saucepan, melt the butter over medium-high heat. Continue to cook until the butter stops bubbling, about 2 minutes. Add the garlic, and swirl the pan,  and continue to cook the garlic for 1 minute. Add about half the flour, and whisk to combine, breaking up any lumps. Add the remaining flour and whisk until smooth and bubbling. Cook the roux, whisking constantly, until it turns light brown and begins to smell slightly toasty, about 2 to 3 minutes. While gently whisking with one hand, slowly stream 2 cups of the warmed milk into the roux. Wish thoroughly to ensure no clumps, and stream in remaining milk while whisking. Add the nutmeg, and bring the mixture to a boil over medium heat, whisking frequently to make sure it is not sticking to the bottom of the saucepan. Once the mixture has come to a boil and thickened (about 7 minutes), remove from the heat and whisk in Parmesan until smooth. Add chopped herbs, salt, and season to taste with black pepper. Assemble lasagna: Mix the cooled spinach mixture with the ricotta mixture until evenly combined.In a 13"-x-9" baking  dish, assemble the lasagna in the following layers: Start with 1 cup of the Mornay sauce. Spread all over the bottom of the pan, covering completely to the edges. Next, layer 6 no-boil noodles over the sauce, overlapping about ½” where necessary. (The long edge of the noodle should align with the long edge of the pan. If your pan has rounded edges, the firm noodles may not fit as neatly into the pan. To help the fit, and reduce unnecessary overlap, gently snap off a small corner of the noodle that would fit into the corner of the pan.) Next, spread 1½ cups of the ricotta-spinach mixture onto the noodles, covering the noodles completely so that it has the moisture it needs to cook through. Add ⅓ cup of cooked chicken, and finish the layer with ⅔ cup of mozzarella. Repeat the layers twice, starting with the sauce and ending with the ⅔ cup of mozzarella cheese. For the top layer of lasagna, spread 1 cup of sauce on top of the last layer’s mozzarella. Cover with 6 no-boil noodles, and top with 1 cup of mozzarella and ⅓ cup of Parmesan. Lightly grease one side of a large piece of aluminum foil. Wrap the lasagna tightly in two layers of foil, with the greased foil facing the lasagna. Bake for 25 minutes, remove the foil and bake uncovered for an additional 15 minutes. Let cool for 30 minutes before serving.