Preheat the oven to a temperature of 350 degrees Fahrenheit (175 degrees Celsius). Concurrently, apply a light coat of non-stick cooking spray or butter to an 8x8 inch baking dish.
In a spacious mixing bowl, combine the shredded zucchini, diced white onion, half of the shredded cheddar cheese, thawed corn, diced jalapeño, eggs, garlic powder, cumin, salt, and black pepper. Ensure that the mixture is thoroughly combined.
Gradually integrate the corn muffin mix into the aforementioned mixture, ensuring a consistent blend.
Transfer the finalized mixture into the previously prepared baking dish. Evenly distribute the remaining cheddar cheese over the surface.
Place the dish in the preheated oven and allow it to bake for approximately 50 to 55 minutes. The casserole is fully cooked when the center is set and the surface exhibits a golden-brown hue. Once done, remove from the oven and serve whilst still warm.