Heat 2 tablespoons of oil in a large skillet over medium heat. Add onion, bell pepper, and zucchini and cook, stirring often, until vegetables are tender, about 10 minutes.
In a medium bowl, whisk together eggs, milk, feta cheese, parsley, salt, and pepper.
Place prepared pie crust in a 9-inch pie plate. Pour remaining oil into crust, then pour in egg mixture. Top with cooked vegetables.
Bake in preheated oven until golden brown and center is set, about 25 minutes.
Let cool before serving.
Interesting Facts
This quiche is a great way to use up leftover vegetables.
You can substitute other vegetables for the zucchini, bell peppers, and onion, such as mushrooms, spinach, or broccoli.