Preheat oven to 375 degrees. Place piecrust on a rimmed baking sheet lined with foil. In a medium skillet over medium heat, drizzle in olive oil. Add garlic and onion and saute until translucent- 5 to 7 minutes. Add spinach, a little at a time, and cook until wilted. Season with salt and pepper and let cool.

In a bowl, whisk eggs and half-and-half. Add lemon zest and thyme. Add spinach, feta, and half the swiss cheese and mix until well combined. Season with salt and pepper. Pour carefully into piecruse and sprinkle remaining swiss cheese evenly over the top. Bake for about 40 minutes or until center is set. Cool at least 10 minutes before serving.