Preheat your oven to 350º.

Grease the bottom and sides of a 13"x9" glass baking dish with vegetable oil or cooking spray.

With a hand grater or food processor, shred zucchini, squash, and onion. Add to a large mixing bowl. To the bowl, add the shredded cheese, eggs, milk, and oil. Stir to combine.

Once combined, add the corn muffin mix and salt and pepper. Stir again to completely incorporate all the ingredients.

Pour into the prepared baking dish and bake on the middle rack of the oven for 1 hour. Serve warm or room temperature, and enjoy!