Preheat oven to 400f degrees. Lightly spray a large baking sheet with nonstick cooking spray or cover with nonstick aluminum foil (for easier cleanup later)
Pat the chicken dry with a paper towel. In a wide, shallow bowl, whisk the egg with a fork. In a separate shallow bowl, combine the Panko bread crumbs, Parmesan cheese, Italian seasoning and garlic salt.
First, dip chicken breast into the egg.
Then dip chicken into the crumb mixture (patting to help coating stick to the chicken).
Repeat this process with the remaining chicken and place prepared chicken onto baking sheet.
In a medium-sized, microwave-safe bowl, melt the butter in the microwave. Toss sliced potatoes into the melted butter and coat thoroughly. Season the potatoes with Italian seasoning and garlic salt. Stir to make sure all of the potatoes are coated.
Place potatoes onto baking sheet (layering them around the chicken.)
Bake chicken for about 25-30 minutes. Chicken should reach an internal temperature of 165f degrees when done.
Once chicken is cooked, remove sheet pan from oven and turn on broiler. Spoon ¼ cup of marinara sauce on top of each piece of chicken. Then top with ¼ cup shredded mozzarella cheese.
Place sheet pan under the broiler (about 3-4 inches away from heat) and broil until cheese is melted. Note: It's super important you don't walk away from your oven when the broiler is on and cooking. Things can get burned super fast if you aren't looking.