Preheat the oven to 375°F. Fit the pie crust into a 9-inch pie dish, crimp the edge if desired, and refrigerate while preparing the filling.

Place the zucchini slices in a colander and toss with 1/2 teaspoon of the salt. Let sit for 10 minutes, then pat dry thoroughly.

Heat the olive oil in a large skillet over medium heat. Add the onion and cook for 4 to 5 minutes until softened.

Add the zucchini, remaining 1/2 teaspoon salt, black pepper, and oregano to the skillet. Cook for 4 to 5 minutes until the zucchini just begins to turn tender. Remove from the heat and cool slightly.

In a medium bowl, whisk together the eggs and sour cream until smooth. Stir in the cheddar, half of the Parmesan, and the chopped parsley.

Spread the zucchini and onion mixture evenly into the chilled pie crust. Pour the egg and cheese mixture over the vegetables and gently distribute evenly. Sprinkle the remaining Parmesan over the top.

Bake for 40 to 45 minutes, until the center is set, the top is golden brown, and the crust is lightly crisp at the edges. If needed, loosely cover the crust edge with foil if it browns too quickly.

Let the pie rest for 10 to 15 minutes before slicing. Garnish with extra parsley and serve warm or at room temperature.