Preheat the oven to 350°F. Remove the pie dough and let it sit at room temperature for 10-15 minutes.
Transfer the pie dough to a 9-inch deep pie dish. Use your fingertips to gently press it firmly into the bottom and sides of the pie plate. Crimp around the edges if desired.
Prick the bottom of the pie crust with a fork. Place the pie dish on a sheet pan and transfer to the oven to bake for 10-15 minutes.
While the crust bakes, heat olive oil in a large skillet over medium heat. Add onions and zucchini and cook for 7-10 minutes, or until the zucchini has softened. Transfer half of the zucchini to the par baked crust.
In a medium-sized mixing bowl, add eggs, milk, salt, pepper, nutmeg, garlic powder, mozzarella, and 4 tablespoons parmesan. Gently whisk to combine.
Pour mixture into crust and top with remaining zucchini and 2 tablespoons of Parmesan.
Bake for 55-60 minutes, or until set in the center. If the edges look too browned, cover the quiche with foil.
Remove from the oven and let cool for 10-15 minutes before slicing and serving. Garnish with fresh chopped basil or parsley, if desired. Enjoy.