Preheat your oven to 375°F (190°C) so it reaches the proper temperature before the lasagna goes in. Preheating is important because it helps the lasagna cook evenly from the moment it enters the oven. While the oven is warming up, lightly grease a medium-sized baking dish with a small amount of olive oil or cooking spray to prevent sticking.

Wash the zucchini thoroughly under cool running water and pat them dry with a clean kitchen towel. Place them on a cutting board and, using a sharp knife or vegetable peeler, slice the zucchini lengthwise into thin strips. Try to keep the slices even and about the thickness of traditional lasagna noodles so they layer neatly and cook evenly.

Place a large skillet on the stove over medium heat and add the olive oil. Allow the oil to warm for about 30 seconds so it spreads easily across the pan. Swirl the pan gently to coat the bottom, which prevents vegetables from sticking and helps them cook evenly.

Add the sliced mushrooms to the skillet in a single layer. Let them cook for a few minutes without stirring too much so they begin to brown. Mushrooms release moisture as they cook, so allow that liquid to evaporate while stirring occasionally. Continue cooking for about 5–6 minutes, until the mushrooms become tender and develop a deeper golden color and rich flavor.

Add the minced garlic to the mushrooms and stir gently so it doesn’t burn. Immediately add the fresh spinach and cook for another 2–3 minutes, stirring occasionally. The spinach will shrink quickly as it wilts. Continue cooking until the spinach is soft and evenly mixed with the mushrooms, then remove the skillet from heat.

In a separate mixing bowl, add the ricotta cheese, eggs, grated parmesan cheese, salt, black pepper, and Italian seasoning. Using a spoon or spatula, mix everything together until the ingredients form a smooth and creamy mixture. Make sure the eggs are fully blended so the filling bakes evenly and helps hold the lasagna layers together.

Take your prepared baking dish and spread a thin, even layer of marinara sauce across the bottom. This first layer of sauce prevents the zucchini from sticking to the dish and also adds moisture to the base of the lasagna.

Begin assembling the lasagna by placing a layer of zucchini slices over the sauce, slightly overlapping them so they cover the bottom completely. Next, spread a portion of the mushroom and spinach mixture evenly over the zucchini. Add a layer of the ricotta mixture on top, gently spreading it with a spoon. Spoon a small amount of marinara sauce over the ricotta, then sprinkle a handful of shredded mozzarella cheese.

Continue repeating the layers in the same order — zucchini slices, mushroom and spinach mixture, ricotta mixture, marinara sauce, and mozzarella cheese. Keep building layers until all the ingredients are used, finishing with a generous layer of mozzarella on top so it melts and forms a golden crust.

Place the assembled baking dish into the preheated oven and bake for 35 to 40 minutes. As it cooks, the cheese will melt and bubble while the flavors blend together. You’ll know it’s ready when the top becomes lightly golden and the edges of the sauce start bubbling.

Remove the lasagna carefully from the oven and place it on a heat-safe surface. Allow it to rest for about 10 minutes before slicing. This resting time helps the layers set, making it easier to cut clean slices while keeping the lasagna warm and delicious when served.