Preheat oven to 375 degrees F. Coat a 2-quart baking dish with cooking spray. In a medium saucepan over medium heat, combine chicken broth, cream cheese, Cheddar cheese, and pepper. Whisk until smooth, 4 to 6 minutes.
Stir the pierogies into the mixture and pour into prepared baking dish. Bake 25 to 30 minutes, or until bubbly. Sprinkle with bacon and scallions; serve immediately.