Preheat oven to 375°F (190°C). Grease a large baking dish with nonstick spray.

In a skillet over medium heat, sauté sliced mushrooms and minced garlic in olive oil until golden brown (about 5 minutes).

In a bowl, mix ricotta cheese, half of the mozzarella, Parmesan cheese, salt, and pepper until well combined.

Start layering: Spread some diced tomatoes at the bottom of the baking dish, place three lasagna noodles side by side, add half of the sautéed mushrooms and spinach, then top with half of the cheese mixture.

Repeat layering until all ingredients are used up, finishing with noodles topped generously with remaining mozzarella cheese.

Cover with aluminum foil and bake for 25 minutes. Remove foil and bake for an additional 15–20 minutes until golden brown. Allow to cool slightly before serving.