Preheat your oven to 350°F (175°C). Thaw the frozen pie crust completely and poke holes in the bottom to prevent bubbling. Pre-bake crust for about 10 minutes.

In a medium bowl, whisk together four room-temperature eggs and season with salt and pepper.

Sauté one finely chopped onion in olive oil for 3-5 minutes until soft. Add two cups of fresh spinach and cook until wilted.

Layer sautéed onions in the pre-baked crust, followed by wilted spinach, shredded cheddar cheese, and crumbled feta cheese.

Pour the egg mixture over the layered ingredients, ensuring even coverage.

Bake the quiche in the oven for about 24-30 minutes until the filling is puffed and slightly jiggles in the center.

Allow the quiche to cool for 5-15 minutes before slicing and serving.