Preheat the oven to 375°F. Take the defrosted pie crust and lightly roll it out. Lay it into the 9 inch baking dish, poke some holes into it with a fork, then place into the oven. Bake for 10 minutes and remove. Set aside.

In a medium bowl, mix eggs, milk, salt and pepper with a whisk; set aside.

Add the chopped spinach and chopped onions to the bottom of the pie crust. Add the grated cheddar cheese over the top and then sprinkle the feta crumbles over the top. Pour the egg mixture evenly throughout the pie crust.

Place the spinach quiche into the pre-heated oven. Bake at 375 degrees for 40-50 minutes or until the center is set. Remove from oven and let rest for 15 minutes before slicing and serving.