Melt 2 tablespoons butter in a large saucepan over medium-high heat. Cook squash and onions until tender. Remove from heat, and stir in Cheddar cheese, mayonnaise, eggs, and crackers. Season with Ranch dressing mix and salt.
Spread the squash mixture into a medium baking dish. Mix together stuffing and 1/2 cup melted butter, and sprinkle over the squash mixture.
Bake 20 to 30 minutes in the preheated oven, or until firm and lightly browned.