Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish.

In a large skillet, heat 1 tablespoon each of butter and olive oil over medium heat. Add the chopped onion and sauté for about 3 minutes.

Add finely minced garlic to the skillet and cook for an additional 30 seconds. Introduce the sliced zucchini and cook for about 5–6 minutes until slightly tender.

Stir in the corn and continue cooking for an additional 2 minutes, then remove the skillet from heat and set it aside to cool slightly.

In a large mixing bowl, whisk together the shredded cheddar cheese and half of the grated Parmesan cheese until combined.

Fold the cooled vegetable mixture into the cheese blend.

Carefully transfer the combined mixture into the prepared baking dish, spreading it out evenly.

In a small bowl, combine the crushed crackers with the remaining Parmesan cheese and sprinkle it over the top of your casserole.

Place the baking dish in the preheated oven and let it bake for 35–40 minutes.

Once baked, remove the casserole from the oven and allow it to rest for about 10 minutes, then garnish with fresh parsley.