Spray your baking dish with oil. Preheat your oven to 350°.
Wash your veggies and peel your onion.
Slice your zucchini and squash. Chop your onion.
Add your chop onion to the bottom of your baking dish.
Transfer your sliced zucchini and squash onto of your bed of onions.
Add 2 tbsp of garlic onto and in between your sliced veggies.
Add your garlic powder, onion powder, black pepper, and garlic parmesan on top of the veggies.
Add your butter ontop arranging in different places. Next add your parmesan cheese all over.
Cover and bake for 20 minutes.
Uncover and bake for a few more minutes allowing the top to brown a little.