Preheat oven to 350°F.
Combine spinach, ricotta, Parmesan cheese, 1 cup mozzarella cheese and eggs in a medium bowl. Stir in mushrooms. Set aside.
Combine tomato sauce and spaghetti seasoning.
Grease a 13x9-inch baking pan. Line with a single layer of lasagna noodles. Top with half of spinach/cheese mixture and half the seasoned tomato sauce. Repeat. Sprinkle remaining 1 cup mozzarella cheese over the top. Cover with foil.
Bake 25 minutes. Remove foil and continue baking 10 minutes. Remove from oven. Let rest 10 minutes before cutting for easy serving.