In large pan, cook onion ... in oil. Add pasta sauce; simmer 15 minutes. In bowl, mix ricotta, spinach, 1 cup mozzarella, parmesan ... until cheese is melted.
Cook shells, following package directions ... simmers, squeeze thawed spinach. In large bowl, beat ... the chopped spinach, ricotta and Mozzarella cheese, onion salt, ... bake 20 minutes more.
Save 1 cup Mozzarella cheese ... spaghetti sauce. Mix spinach, cheeses, eggs and salt. Stuff pasta shells with above mixture. Cover ... 350°F for 1 hour.