Preheat the oven to 375°F (190°C).
Heat olive oil in a pan and lightly fry the chopped mushrooms.
Add garlic powder, salt, and pepper. Cook until the mushrooms are tender and the flavors are well combined.
If using dried lasagna noodles, cook them according to package directions in very salty water until 5 minutes less than al dente. Drain and set aside. Lay the noodles out in a single layer on a lightly oiled baking sheet to prevent sticking.
Pour about 2 tbsp of béchamel sauce into the bottom of an oven-safe pan to coat the bottom.
Place a layer of lasagna noodles on top.
Dollop 1/3 of the spinach, mushroom, and cheese mixture over the noodles and spread evenly. Follow with 4 tbsp of béchamel sauce.
Repeat the layering process two more times.
Finish with a final layer of noodles, the remaining béchamel sauce, and sprinkle with mozzarella and Parmesan cheese.
Cover with foil and bake for 30 minutes.
Remove the foil and bake for an additional 10 minutes, or until the top is browned and bubbly. Optionally, broil for a few minutes to get a crisp top, but watch closely to prevent burning.