Place the pie crust in the pie plate and bake at 325° F for 12 minutes. Remove from oven and set aside.
Meanwhile, gather all of the other ingredients and prepare them. Chop the bacon, dice the onion, shred the cheese, etc.
In a 4-cup glass measuring cup or a bowl, whisk together the eggs, half and half, salt, pepper, and cayenne. Set aside.
Add 3/4 of the bacon, half of the scallions, onion, and 3/4 of the cheese to the pre-baked pie shell.
Pour the egg mixture over the ingredients in the pie shell.
Arrange the remaining bacon, cheese, and scallions over the top.
Bake for 40-50 minutes, or until center is set and the top is a light golden color, and a knife inserted into the center comes out clean.
Remove from oven to a wire rack to set for 10 minutes before slicing and serving.