Pre-heat oven to 375 degrees.
Cut the cooked bacon strips into smaller pieces. If using cold cooked bacon then microwave for 25 seconds to warm them up. Set aside.
In a pan add over medium heat, melt the butter then add in the chopped onions. Cook the onions until translucent. Add in the spinach and reduce the heat to medium low. Cook the spinach until a little more than halfway wilted. Then turn off the heat and continue to cook the spinach in the residual heat until they are all wilted. This prevents the spinach from becoming over cooked and mushy.
Once they are all wilted, transfer the spinach to a plate and let cool.
In the meantime, shred the cheese and set aside.
Place the pie crust on a baking tray covered with aluminum foil to prevent spillage.
Place the spinach on the bottom of the pie crust then add on the bacon. Save a handful of the bacon pieces to place on top of the quiche later. Also add a handful of the shredded cheese. We will add the rest of the cheese later.
Crack the eggs into a bowl, add in 1/4 teaspoon of salt & 1/8 teaspoon black pepper and whisk.
Then pour in the half & half and stir.
Pour the egg mixture over the spinach and bacon pieces. Then add the rest of the shredded cheese and top with the remaining bacon pieces.
Transfer to the oven and place on the second level. Bake for 40 minutes at 375 degrees.
Then turn the heat up to 425 for 10-15 minutes or until the top of the pie is golden brown.