Preheat oven to 350°F.
Combine spinach, ricotta, 1 cup mozzarella cheese, Parmesan cheese, eggs, Italian herb seasoning, garlic powder, salt and pepper in medium bowl. Stir in mushrooms. Set aside.
Grease a 13 x 9-inch pan. Line with a single layer of lasagna noodles. Top with half of spinach/cheese mixture. Pour half of spaghetti sauce over all. 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.