Step 1: Preheat your oven to 375°F (190°C). Prepare your 9-inch pie crust by fitting it into a pie plate. Trim and crimp the edges as desired.
Step 2: Blind bake the pie crust. Line the crust with parchment paper and fill with pie weights, dried beans, or rice. Bake for 10-12 minutes, or until the edges are lightly golden. Remove the weights and parchment, then return to the oven for another 5 minutes to fully dry out the bottom. Let cool slightly.
Step 3: Grate the zucchini using the large holes of a box grater. Place the grated zucchini in a colander, sprinkle generously with 1 teaspoon of salt, and let sit for 15-20 minutes. Firmly squeeze out as much liquid as possible from the zucchini using a clean kitchen towel or strong paper towels.
Step 4: In a large mixing bowl, combine the thoroughly drained grated zucchini, chopped onion, minced garlic, and fresh parsley. Mix well.
Step 5: In a separate medium bowl, whisk together the eggs, milk, grated Parmesan cheese, shredded cheddar cheese, all-purpose flour, black pepper, and dried oregano. Whisk until well combined and smooth.
Step 6: Add the zucchini mixture to the egg and cheese mixture. Stir gently until all ingredients are thoroughly incorporated.
Step 7: Pour the entire filling mixture into your blind-baked pie crust. Spread it evenly with a spatula.
Step 8: Bake the zucchini pie in the preheated oven for 45-55 minutes, or until the center is set and the top is golden brown. If the crust edges brown too quickly, cover them loosely with aluminum foil.
Step 9: Once baked, remove the pie from the oven and let it cool on a wire rack for at least 15-20 minutes before slicing and serving. This allows the filling to set completely.