Preheat your oven to 375°F (190°C).

In a mixing bowl, combine all-purpose flour, salt, black pepper, and fresh oregano. Add olive oil and cold water gradually, mixing until a dough forms. Lightly flour your hands and press the dough into a 9-inch quiche pan.

Place the crust in the preheated oven and bake for 8–10 minutes, or until it turns lightly golden.

Heat olive oil in a skillet over medium heat. Add diced onion and minced garlic, sautéing until softened. Fold in the fresh spinach and wilt for 2 minutes, then set aside.

In a large bowl, whisk together the large eggs, milk or cream, Greek yogurt if using, Italian seasoning, nutmeg, salt, and pepper. Stir in the crumbled feta cheese and sautéed vegetables.

Pour the custard filling into the pre-baked crust, spreading evenly.

Return the quiche to the oven and bake for 30–35 minutes, until the custard is set and the top is golden brown.

Allow the quiche to cool for 5–10 minutes before slicing and serving warm.