Prepare the ricotta mixture by combining the ricotta cheese, 1/4 cup of mozzarella cheese, 2 tbsp freshly grated Parmesan cheese, a small egg, fresh parsley, a dash of freshly grated nutmeg, sea salt, and freshly cracked pepper, to taste. Stir until well combined; set aside. Prepare the onion and spinach by heating 1/2 tablespoon of butter in a large skillet over medium heat. Add the onion and cook, stirring occasionally, for 4-5 minutes.
Add the baby spinach and a pinch of crushed red pepper flakes.
Cook, stirring constantly, for 1 minute, until the spinach is just starting to wilt.
Remove from the heat and season with sea salt and freshly cracked pepper, to taste. Pour into a bowl; set aside.
Prepare the mushrooms by heating 1 tablespoon of butter in the same large skillet over medium-high heat.
Add the mushrooms and cook, stirring very rarely, for 3-4 minutes.
Add the minced garlic and season with sea salt and freshly cracked pepper, to taste, then cook, stirring constantly, for 1 minute.
Remove from the heat. Pour into another bowl; set aside.
Prepare the white sauce by heating the remaining 2 1/2 tablespoons of butter in the same large skillet over medium-high heat.
Add the flour to the melted butter then stir with a whisk for 1-2 minutes, stirring constantly.
Slowly add the milk to the skillet while continuously whisking.
Cook and whisk over medium heat until bubbly and thickening.
Season with a dash of freshly grated nutmeg and sea salt and freshly cracked pepper, to taste. Remove from the heat.
Preheat the oven to 375 degrees. Coat an 8 x 8 inch or small baking dish with cooking spray.
Prepare the lasagna by spooning some sauce into the bottom of the pan.
Place a layer of no-bake lasagna noodles (or cooked noodles if you prefer) on the bottom of the dish.
Spread some of the ricotta mixture onto the noodles followed by half of the spinach.
Next, add half of the mushrooms, then a light sprinkling of mozzarella cheese.
Place another layer of noodles and repeat the process using up the remaining ingredients.
Place the third and final layer of noodles followed by the remaining white sauce.
Sprinkle the top with more shredded mozzarella and a bit of freshly grated parmesan.
Place into the oven and bake for 35-40 minutes, or until it's bubbling and the top is starting to become golden brown.
Remove from the oven and allow to cool for 10-15 minutes before sprinkling the top with fresh parsley.
Slice and serve. Enjoy!