In a large saucepan cook pasta according to package directions; drain. Rinse pasta with cold water; drain again.
Meanwhile, in a large skillet cook carrots, zucchini, and onion in hot oil over medium-high heat 3 to 5 minutes or until tender. Stir in spinach; cook and stir 1 minute. Transfer spinach mixture to a large bowl.
Stir ricotta cheese, 1 cup of the shredded cheese, and salt into vegetable mixture. Spoon 2 rounded Tbsp. cheese mixture into each pasta shell. Place pasta sauce in skillet; place filled shells in sauce. Heat shells and sauce, covered, over medium heat 10 minutes or until heated through. Sprinkle with remaining shredded cheese before serving.