Place 12 large eggs in a large saucepan; add water to cover by 1-inch.
Bring the water to a boil, cover, and remove from heat. Let the eggs
sit for 10 minutes. Drain the water and transfer the eggs to a bowl of
ice water and let them cool completely. Peel the eggs, halve them
lengthwise and remove the yolks.
Coarsely chop the bacon and cook in a medium skillet over medium heat
until browned and crisp. Transfer the bacon to paper towel and strain
the drippings through a fine-mesh sieve into a small bowl. Set aside
the bacon fat.
Finely mash the reserved egg yolks, bacon fat, mayonnaise, Dijon
mustard, and scallions in a medium bowl; season with salt and pepper.
Transfer the yolk mixture to a piping bag equipped with a large plain
tip and pipe the mixture into the egg white halves.