Preheat the oven to 375°F (190°C). Cook the lasagna noodles according to package instructions until al dente. Drain and set aside.

In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté for about 3-4 minutes until translucent. Stir in the minced garlic and cook for another minute.

Add the sliced mushrooms, thyme, oregano, salt, and pepper to the skillet. Cook for about 5-7 minutes until the mushrooms are tender and any liquid has evaporated. Remove from heat and let cool slightly.

In a mixing bowl, combine the ricotta cheese, egg, and half of the mozzarella cheese. Mix well until smooth.

Spread a thin layer of marinara sauce on the bottom of a 9x13 inch baking dish. Layer 3 lasagna noodles over the sauce. Spread half of the ricotta mixture over the noodles, followed by half of the mushroom mixture, and a third of the marinara sauce. Repeat the layers, finishing with a final layer of noodles topped with the remaining marinara sauce and the rest of the mozzarella and Parmesan cheese.

Cover the dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 15-20 minutes or until the cheese is bubbly and golden.

Let the lasagna cool for about 10 minutes before slicing. Garnish with fresh parsley before serving.