Butterfly your chicken breasts - hold your hand on top of the chicken breast and slice into the side of the chicken breast, cutting from one side to the other, leaving the opposite side intact. Your goal is to create a pocket for your filling. If needed, pound chicken breasts to create even thickness. entire breast (closed) should be no more than 1 inch in thickness.
In a cast iron skillet, cook bacon according to package directions. Drain all but 2 tablespoons of bacon grease. Set aside.
Season chicken breasts with garlic powder and pepper. Stuff chicken breasts with spinach, mozzarella cheese, and bacon. Optionally, use toothpicks to keep the chicken breasts closed around the open edge.
Heat skillet over medium heat. Sear chicken breasts on each side for 2-3 minutes per side, until browned.
Move skillet to oven to finish cooking for 12-15 minutes, or until juices run clear.
Remove from oven and allow to rest for 2-3 minutes before serving.
If you choose to omit bacon from this recipe - use 2 tablespoons of unsalted butter in your pan, and season chicken breasts with ½ teaspoon of salt before cooking.