1. Preheat oven to 350°. Cut squash into 1/4-inch-thick slices; place in a Dutch oven. Add onion, 1 tsp. salt, and water to cover. Bring to a boil over medium-high heat, and cook 5 minutes; drain well, and pat squash dry with paper towels.
2. Stir together grated carrots, next 3 ingredients, and remaining 1/2 tsp. salt in a large bowl; fold in squash mixture. Spoon into a lightly greased 2-qt. oval baking dish.
3. Stir together cornflakes and next 3 ingredients in a small bowl. Sprinkle over squash mixture.
4. Bake at 350° for 30 to 35 minutes or until bubbly and golden brown, shielding with aluminum foil after 20 to 25 minutes to prevent excessive browning, if necessary. Let stand 10 minutes before serving.