Preheat your oven to 375°F (190°C).

Cook the lasagna noodles according to the package instructions until al dente, then drain and set aside.

Heat the olive oil in a large skillet over medium heat. Add the chopped onion and garlic, sautéing until fragrant and the onion is translucent.

Stir in the sliced mushrooms, and cook until they are browned and tender. Add the chopped spinach, dried thyme, salt, and pepper. Cook until the spinach wilts down, about 3-4 minutes.

In a mixing bowl, combine the ricotta cheese with a pinch of salt and pepper.

In a baking dish, start layering. Begin with a thin layer of marinara sauce, followed by noodles, the ricotta mixture, sautéed vegetables, and a sprinkle of mozzarella. Repeat the layers, finishing with a top layer of noodles topped with 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 top is golden and bubbly.

Allow the lasagna to cool for at least 10 minutes before slicing.