In a large skillet, heat the olive oil over medium heat. Add the minced garlic and sauté for about 1 minute until fragrant.
Add the sliced mushrooms to the skillet and cook for 5-7 minutes until they release their moisture and begin to brown.
Stir in the chopped spinach, salt, black pepper, and Italian seasoning. Cook for an additional 3-4 minutes until the spinach wilts. Remove from heat and set aside.
In a separate saucepan, melt the butter over medium heat. Once melted, whisk in the flour and cook for about 1 minute until bubbly.
Gradually add the milk to the saucepan, whisking continuously until the mixture is smooth and begins to thicken, about 5-6 minutes.
Remove from heat and stir in the ricotta cheese and grated parmesan until fully combined. Season with salt and pepper to taste.
Preheat your oven to 375°F (190°C).
In a 9x13 inch baking dish, spread a thin layer of the creamy sauce on the bottom. Place 3 cooked lasagna noodles over the sauce.
Spread half of the mushroom and spinach mixture over the noodles, followed by a layer of the creamy sauce and a third of the shredded mozzarella cheese.
Repeat the layers with another 3 noodles, the remaining mushroom and spinach mixture, more creamy sauce, and half of the remaining mozzarella cheese.
Top with the final 3 noodles, the last of the creamy sauce, and the remaining mozzarella cheese.
Cover the dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 15-20 minutes until the cheese is bubbly and golden brown.
Once baked, remove from the oven and let it cool for 10 minutes before slicing. Garnish with fresh parsley before serving.