Heat a large skillet over medium heat and add a drizzle of olive oil. Sauté the diced onion and minced garlic until translucent, about 3-4 minutes.
Add the sliced mushrooms and cook until softened, about 5 minutes.
Stir in the chopped spinach and cook until wilted, about 2 minutes. Season with salt, pepper, oregano, and basil. Remove from heat.
In a large bowl, combine the cooked, shredded chicken with half of the marinara sauce.
In another bowl, mix the ricotta cheese with a pinch of salt and pepper.
Preheat the oven to 375°F. Spread a thin layer of marinara sauce on the bottom of a 9x13-inch baking dish.
Place 3 lasagna noodles over the sauce. Spread half of the chicken mixture over the noodles, followed by half of the sautéed vegetable mixture, and half of the ricotta mixture. Sprinkle with 1 cup of mozzarella cheese.
Repeat the layers: 3 noodles, remaining chicken mixture, remaining sautéed vegetables, remaining ricotta, and another cup of mozzarella.
Top with the last 3 noodles, the remaining marinara sauce, and the remaining mozzarella and Parmesan cheese.
Cover the dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and golden.
Let it cool for 10 minutes before slicing.