Heat 1 tbsp (15ml) of olive oil in a large skillet over medium-high heat. Add sliced cremini mushrooms in an even layer. Let sear undisturbed for 4-5 minutes until a deep golden-brown crust forms. Toss, season with salt and pepper, cook until moisture evaporates, and transfer to a bowl.

In the same skillet, add remaining 1 tbsp (15ml) olive oil and minced garlic. Cook 30 seconds. Add fresh spinach, tossing until just wilted. Remove from heat. Once cool, squeeze out all excess liquid completely in a clean towel.

Melt butter in a saucepan over medium heat. Whisk in flour to create a roux, cooking for 1-2 minutes. Gradually whisk in whole milk until smooth. Simmer until thickened. In a separate bowl, mix ricotta cheese with salt and pepper.

Spread a thin layer of béchamel in the bottom of a 9x13-inch white rectangular ceramic casserole dish. Lay down 3-4 boiled ruffled lasagna noodles. Spread a layer of ricotta, followed by browned mushrooms and wilted spinach. Drizzle with béchamel, sprinkle with mozzarella, and repeat.

Top the final layer of noodles with remaining béchamel, then an even, heavy layer of melted mozzarella and parmesan cheese. Cover loosely with foil and bake at 375°F (190°C) for 35 minutes. Remove foil and bake 10-15 more minutes until the top is bubbly, golden-brown, and slightly charred at the edges. Garnish with chopped fresh parsley and coarse black pepper. Let rest 15 minutes before slicing.