1. Preheat the oven to 350°F and lightly grease a 13 x 9-inch baking dish.

2. Slice the yellow squash and zucchini into thin rounds.

3. Place the squash, zucchini, chopped onion, and 2 teaspoons of salt in a large pot.

4. Cover the vegetables with water and bring to a boil over medium-high heat.

5. Cook for about 5 minutes, then drain the vegetables thoroughly.

6. In a large mixing bowl, combine the grated carrots, cream of chicken soup, sour cream, chopped water chestnuts, and remaining 1/2 teaspoon salt.

7. Fold the cooked squash mixture into the creamy filling until evenly combined.

8. In a separate bowl, mix the herb-seasoned stuffing with the melted butter.

9. Spread half of the stuffing mixture across the bottom of the prepared baking dish.

10. Spoon the squash mixture evenly over the stuffing layer.

11. Top with the remaining buttered stuffing mixture.

12. Bake for 30 to 35 minutes, or until the filling is bubbly and the top is golden brown.

13. If the topping browns too quickly, loosely cover the casserole with foil during the final 10 to 15 minutes.

14. Let the casserole rest for 10 minutes before serving.