Preheat the oven to 400°F. Position a large baking sheet on the center oven rack to heat as the oven preheats.

Place a sheet of parchment paper on a flat surface. One at a time, place a chicken breast inside a zip-top bag, press out the air, and seal. Using a rolling pin or meat mallet, pound each piece to an even 1/2-inch thickness. Transfer the flattened chicken to the parchment. Repeat for all breasts. Season both sides with kosher salt and black pepper.

In a mixing bowl, stir together the cream cheese and mayonnaise until a uniform consistency is achieved. Fold in the cheddar cheese, crumbled bacon, toasted almonds, garlic powder, and half of the sliced green onions.

Evenly spread the prepared cheese mixture over the top of each seasoned chicken breast. Carefully remove the preheated baking sheet from the oven and place it on a stable, heat-resistant surface. Lift the parchment edges and gently transfer the topped chicken pieces onto the hot pan.

Bake for 10 to 15 minutes, or until the cheese topping is melted and the internal temperature of the chicken reaches 165°F. Let the chicken rest for 5 minutes before garnishing with the remaining sliced green onions.