Step 1

Preheat oven to 400 degrees F (200 degrees C).

Step 2

Fit pie crust into a 9-inch pie dish.

Step 3

Whisk eggs, milk, parsley, garlic, salt, black pepper, and nutmeg in a bowl.

Step 4

Gently combine spinach, mushrooms, onion, and feta cheese in a separate bowl. Spread spinach-mushroom mixture in the prepared pie dish; top with half the Swiss cheese.

Step 5

Pour egg mixture evenly over the filling, swirling egg mixture in bowl to spread seasonings through the eggs; top the quiche with remaining Swiss cheese. Place quiche on a baking sheet.

Step 6

Bake in preheated oven until the quiche is lightly puffed and browned, 45 to 50 minutes. A toothpick inserted into the center of the filling should come out clean. Cool for 30 minutes before serving.