Preheat your oven to 375°F (190°C). Gather your ingredients.

In a skillet, heat olive oil over medium heat. Sauté chopped onion for about 5 minutes, then add minced garlic and spinach for another 3 minutes.

In a mixing bowl, whisk together eggs, heavy cream, oregano, salt, and pepper. Fold in the cooled spinach mixture and crumbled feta.

Transfer the pie crust to a pie dish and pour the filling into the crust, spreading it evenly.

Bake in the preheated oven for 35 to 40 minutes, until the center is set and the top is golden-brown.

Let the quiche cool for about 10 minutes before serving warm or at room temperature.