In a medium bowl, whisk the eggs with a little salt and pepper and set aside. Preheat the oven to 350º F.

Heat a large, oven-safe skillet on high heat. Add the bacon pieces and cook until golden brown. Reduce the heat to medium, remove the bacon, and set aside.

To the same skillet, add diced onion and cook for about 5 minutes, until it starts to soften. Add spinach and a little salt. Cook for about 3 minutes. (Note: the liquids from the spinach will help to deglaze the pan.) Remove the skillet from the heat.

Pour the eggs over the spinach. With the help of a spoon or spatula, try to break up the clumps of spinach so that the egg mixture covers the spinach evenly.

Sprinkle the bacon and feta cheese crumbles on top.

Bake for about 15 minutes, until the eggs are cooked through.