While this recipe calls for summer vegetables, my brother and SIL prepared it for Christmas dinner 2009 and I loved it. Good as a vegetarian main dish or a side. It's not quite the same as other vegetable gratins already on RecipeZaar. Personally, I would make this with less olive oil, the amount of which I specified in the ingredients, but you can use the original amount if you prefer (just convert teaspoons to tablespoons). This can also be made ahead after assembly and before baking. Just pre-heat the oven. Try to buy the zucchini and squash of roughly the same diameter. I might serve this with bread to soak up the juices. To make this vegan, omit the parmesan cheese. They found this recipe on America's TV test kitchen.