Preheat oven to 350F. Remove the pie dough and allow to sit at room temperature while you prep your ingredients.
Roll the dough out on a well-floured work surface until it’s approximately 12- inches in diameter.
Transfer it to a 9-inch deep pie dish. Using your fingers, press it firmly into the bottom and sides of the pie plate. Trim off any excess, leaving about 1/2-inch overhanging. Then fold/crimp the overhanging dough.
Prick the bottom of the pie crust with the tines of a fork. Place crust on a small sheet pan (this makes is much easier to transfer to the oven once it’s filled).
Transfer the pie crust to your pre-heated oven and bake for 10 to 15 minutes, until par-baked. Then remove.
Meanwhile, heat the oil in a large skillet over medium heat.
Add the onion and garlic and sauté 30 seconds. Add the zucchini, ½ teaspoon salt and pepper, to taste and toss to evenly combine.
Cook for 7-8 minutes, stirring every couple minutes, until the zucchini has softened and flavors combined. With a slotted spoon, transfer three-quarters of the zucchini to par-baked crust.
In a medium bowl, add the eggs, milk, ricotta, mozzarella, 2 tablespoons Parmesan, basil and ½ teaspoon salt and pepper, to taste. Using a fork, mix to combine until uniform.
Pour egg mixture into the crust over the zucchini. Top with remaining zucchini and 2 tablespoons Parmesan.
Cover the crust with aluminum foil so it doesn’t burn and place in oven quiche in oven.
Bake 350F 50 minutes to 1 hour, or until set and top is browned.
Remove from oven and allow to cool for at least 10 minutes before slicing and serving. Top with basil, slice into 6 pieces and serve.