Preheat the oven to 350°F and line a cutting board with parchment paper.
Place chicken on parchment paper and season with salt, pepper, and garlic powder.
Optional: Try coating chicken breasts in pork rind crumbs or low-carb breadcrumb replacement to make the chicken extra crispy.
Cut each chicken breast width-wise, almost in half, but not all the way through.
Note: Chicken should resemble and open-book shape.
Place a second sheet of parchment paper over the halved chicken breast and flatten with a rolling pin or mallet.
In a saucepan over medium heat, combine and melt the butter, cream cheese, and mustard.
Spread the mixture onto the open chicken breasts.
Layer ham and cheese slices on top of the mixture.
Fold the top of the chicken back down and close with either a toothpick or twine.
Heat olive oil in a large skillet over medium heat.
Place chicken breasts in skillet and cook until fully done (no longer pink inside).
Place chicken in a large roasting pan and bake for an additional 10–15 minutes.
Note: For crispier chicken, broil for an additional few minutes.
*Optional: Turn on broiler to make the cheese golden brown.
Remove from oven and serve.