That would be the work of Hap Townes, former owner of the late, great eponymous eatery in Nashville. Here's the recipe, as it ran back in 1994:
Shel Silverstein, who used to come to Nashville regularly, liked squash casserole so much, Hap Townes recalls, that one day when Shel arrived to find that the kitchen had run out of it, he fled the restaurant with his hands in the air.
4 tablespoons butter
1 cup chopped onion
4 cups cooked squash, mashed
1 cup grated mild cheese (Hap uses Velveeta)
1 cup milk
1 cup cracker crumbs
1 teaspoon salt
Preheat oven to 350 degrees.
In a large skillet, saute onion in butter over medium heat until it is limp. Remove the skillet from the heat. Add the squash and mix well. Stir in cheese, milk, 3/4 cup of the cracker crumbs, and salt.