Creating the Creamy Spinach Mushroom Lasagna is straightforward if you follow these simple steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Prepare Noodles: Cook the lasagna noodles according to package directions. Drain and set aside.
3. Sauté Vegetables: In a large skillet, heat olive oil over medium heat. Add the chopped onion and minced garlic, sautéing until softened.
4. Add Mushrooms: Add sliced mushrooms to the skillet and cook until they are browned and tender.
5. Add Spinach: Stir in fresh spinach and cook until wilted. Season with salt and pepper. Remove from heat and set aside.
6. Mix Cheese Filling: In a bowl, combine ricotta cheese, ½ cup Parmesan cheese, shredded mozzarella, egg, Italian seasoning, and a pinch of salt and pepper. Mix until well blended.
7. Layering the Lasagna: In a greased 9×13-inch baking dish, spread a thin layer of marinara sauce on the bottom. Layer three lasagna noodles over the sauce.
8. Add Cheese Mixture: Spread one-third of the ricotta mixture over the noodles, followed by half of the vegetable mixture and a drizzle of marinara sauce.
9. Repeat Layers: Add another layer of noodles, repeating the cheese mixture, vegetable mixture, and sauce. Finish with a final layer of noodles topped with remaining marinara sauce and the rest of the mozzarella and Parmesan cheese.
10. Bake: Cover with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 20 minutes, or until the cheese is bubbly and golden.
11. Rest: Once out of the oven, let the lasagna rest for 15 minutes to set before slicing.

These steps provide a clear guide to creating this creamy masterpiece with ease!