Preheat oven to 350°
Thaw and drain spinach.
Sautée onion in olive oil until translucent. Add spinach and continue cooking until moisture is evaporated.
Crack eggs into a mixing bowl and beat well. Add cheese.
Stir in spinach mixture and pour into buttered 9” pie plate.
If using a crust, roll out and prepare crust in pie plate. Prick bottom several times with a fork, and pour quiche mixture into it.
Bake for 30 minutes or until the middle is set.