Preheat your oven to 180°C (350°F). Grease a 9-inch pie dish lightly and line it with the ready-made pie crust.

Heat 2 tablespoons of olive oil in a skillet over medium heat. Add 1 finely chopped small onion and sauté for about 2-3 minutes until softened. Mix in 2 grated zucchinis and cook for an additional 5 minutes. Remove from heat and set aside to cool.

In a large mixing bowl, whisk together 3 large eggs and then add 200ml of whole milk, 1 teaspoon of dried oregano, salt, and pepper to taste. Mix thoroughly until the egg mixture is well blended.

Spread the cooled zucchini and onion mixture evenly over the prepared pie crust. Sprinkle 150g of crumbled feta cheese over the vegetables. Pour the egg mixture over the top.

Place the assembled quiche in the preheated oven and bake for about 35-40 minutes until the edges are golden brown and the center is set.

Remove the quiche from the oven and let it cool for about 10 minutes before slicing.