01 -
Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish with cooking spray or olive oil.
02 -
Bring a large pot of salted water to a boil. Add lasagna noodles and cook until al dente. Drain and set aside.
03 -
Heat olive oil in a large skillet over medium heat. Cook chopped onion until translucent, about 3-4 minutes. Add minced garlic and cook for 1 more minute.
04 -
Add sliced mushrooms, dried thyme, salt, and pepper to the skillet. Cook until mushrooms are tender and moisture has evaporated.
05 -
Stir chopped spinach into the mushroom mixture and cook for 2-3 minutes until wilted. Remove from heat.
06 -
Spread a thin layer of marinara sauce on the bottom of the baking dish. Arrange three noodles over the sauce. Spread half of the ricotta cheese, then half of the mushroom-spinach mixture, and sprinkle one-third of the mozzarella and Parmesan cheeses on top. Repeat layering with remaining noodles, ricotta, mushroom mixture, and cheeses. Finish with remaining marinara sauce.
07 -
Cover the dish with aluminum foil and bake for 25 minutes.
08 -
Remove foil and bake for an additional 10-15 minutes until the cheese is bubbly and golden brown.