Preheat oven to 350°. Cut squash and zucchini into 1/4-inch-thick slices; place in a Dutch oven. Add chopped onion, 2 tsp. salt, and water to cover. Bring to a boil over medium-high heat, and cook 5 minutes; drain well.
Stir together grated carrots, next 3 ingredients, and remaining 1/2 tsp. salt in a large bowl; fold in squash mixture.
Sprinkle 1 cup crushed chips in bottom of a lightly greased 13- x 9-inch baking dish. Spoon squash mixture over crushed chips, and top with remaining chips.
Bake at 350° for 35 minutes or until bubbly and golden, shielding with aluminum foil after 20 to 25 minutes to prevent excessive browning, if necessary. Let stand 5 minutes before serving.