Cook pasta according to package directions. Rinse, drain, and let cool.
In a large saucepan, heat broth to boiling. Stir in carrots, potatoes and onions and cook 3-4 minutes until vegetables are tender.
Drain vegetables well. (You can mash these up a bit if that's what it takes to hide the veggies!) Combine with ricotta, mozzarella and Parmesan cheese in a large bowl. Stir in Italian seasoning. Fill each cooked and cooled shell with this cheese mixture.
Pour 1/2 cup of the spaghetti sauce in the bottom of a 9x13" baking pan. Arrange stuffed shells in a single layer on the sauce. Pour remaining sauce over top. Sprinkle with additional Parmesan cheese.
To freeze, refrigerate at this point until cold. Then wrap, label, and freeze up to 3 months. To thaw and reheat, thaw whole casserole overnight in refrigerator. Bake as directed below, adding 15-20 minutes to baking time. To thaw and reheat individual shells, microwave on 40% power for 2-4 minutes until thawed. Then microwave on 60% power for 1-3 minutes until hot and bubbly.
Cover with foil and bake at 350°F for 20-30 minutes or until hot and bubbly.