Steam spinach until tender; press out excess moisture and chop coarsely.= Chop mushrooms and onions and mince garlic over medium-high heat until onions are tender; drain excess liquid and cool. Mix ricotta cheese, 2/3 cup Parmesan, egg, salt, pepper, basil and oregano in large bowl. Add cooled spinach and mushroom-onion mixture and mix on low speed until just blended. Cook lasagna according to package directions; rinse under cool water and drain thoroughly. Place foru lasagna strips in bottom of lightly oiled 9x13" pan, overlapping slightly. Top with 2 c of spinach filling. Sprinkle with 1-1/2 c shredded cheese and 1/3 c Parmesan. Repeat layering two more times and top with remaining four lasagna strips. Spread 1 cup of marinara or tomato-cream sauce over top and cover tightly with foil. Preheat oven to 350~ and bake, covered, for 1 hour. Remove from oven and keep warm at least 30 minutes before cutting. Top with extra Parmesan cheese. (Can be refrigerated a day in advance of baking if desired.)