Oven Setup: Start by heating your oven to 375°F (190°C). Follow the instructions on the package to boil the lasagna noodles. Once cooked, drain the noodles and set them aside.
Cook Salmon: In a large skillet, heat the olive oil over medium heat. Season the salmon with salt and pepper, then cook until it flakes easily with a fork, about 4-5 minutes per side. Remove from the skillet and flake into bite-sized pieces.
Sauté Vegetables: In the same skillet, add garlic and onion, sauté until fragrant and translucent. Add the spinach and cook until wilted. Pour in the white wine and cook for an additional 2 minutes. Set aside.
Prepare Béchamel Sauce: In a medium saucepan, melt the butter over medium heat. In a pan, continuously whisk the flour for about 2 minutes to create a smooth roux. Slowly whisk in the milk until smooth. Cook, stirring continuously, until the sauce thickens. Enhance your béchamel sauce by seasoning it with nutmeg, salt, and pepper according to your taste preferences.
Layering the Lasagna: Begin assembling your lasagna by coating the bottom of a 9x13 inch baking dish with a thin layer of the béchamel sauce. Place a layer of lasagna noodles over the sauce, followed by a layer of flaked salmon, sautéed vegetables, ricotta cheese, mozzarella, and Parmesan. Repeat layers, ending with a final layer of noodles and béchamel sauce. Top with remaining mozzarella and Parmesan.
Initial Baking: Cover the baking dish with aluminum foil and place it in the oven for 30 minutes. After 30 minutes, remove the foil and continue to bake for another 15 minutes, or until the cheese topping turns golden and bubbles.
Cooling and Serving: Allow the lasagna to rest and settle for about 10 minutes before cutting into it. Garnish with fresh parsley and serve.