In a large skillet, cook beef with onion, salt, pepper and garlic powder until the onion is tender; drain. Stir in spaghetti sauce, tomato sauce, tomato paste and mushrooms; simmer 10 minutes. Combine the spinach, noodles, eggs, bread crumbs and cheddar cheese; place half in a greased 9 x13 baking dish. Top with half of the meat sauce. Repeat layers.Cover and bake at 180ÂșC or 40 to 45 minutes or until hot and bubbly. Sprinkle with mozzarella cheese; let stand 10 minutes.