Preheat oven to 350°. Spray a 2-quart baking dish with cooking spray.
In a large Dutch oven, bring broth, squash, zucchini, and onion to a boil over medium-high heat. Reduce heat, and simmer until squash is tender, about 7 minutes. Drain well.
In a large bowl, stir together 1½ cups cheese, bell pepper, egg, soup, sour cream, melted butter, salt, and pepper. Gently stir in cooked vegetables until well combined. Spoon half of squash mixture into prepared pan. Sprinkle with half of crushed crackers. Top with remaining squash mixture, remaining crackers, and remaining ½ cup cheese.
Bake until hot and bubbly and cheese is melted, about 25 minutes. Let stand for 10 minutes before serving.
Recipe by Paula Deen Magazine at https://pauladeenmagazine.com/cheesy-squash-and-zucchini-casserole-recipe/