Prepare your chicken by cutting larger pieces in half, if necessary. Thicker pieces may need to be butterflied or pounded lightly with a mallet until about 1/2 inch thick. Season with salt and pepper.
Set up your breading station but pouring the panko bread crumbs into a shallow bowl and add the Parmesan, 1 tablespoon Italian seasoning, 1 teaspoon garlic powder, and 1 tablespoon parsley flakes. Whisk together to combine. In another shallow bowl, whisk one egg.
Dip your chicken pieces into the egg and let the excess drip off. Then place the chicken into the breadcrumb mixture. Coat both sides with the panko. Place on a plate and continue with the rest of the chicken.
Heat the 2-3 tablespoons of olive oil in an oven-safe large skillet (or cast iron skillet) on medium-high heat. Add chicken pieces a few at a time, do not overcrowd as this will result in a mushy coating not crispy. You will brown the chicken on both sides, about 2 – 3 minutes on each side or until golden brown. Remove from the skillet and place on a platter. Set aside.
Reduce temperature to medium. At this point, wipe out your skillet with a paper towel to remove the excess oil. Pour your spaghetti sauce into the same skillet and add the remaining 1 tablespoon of Italian seasoning, 1 teaspoon of garlic powder, and 1 tablespoon of parsley flakes. Stir to combine.
Add all the chicken back into the skillet and cover. Let simmer for about 20 minutes until the chicken is tender and cooked through.
While the chicken is cooking, cook your pasta according to the package directions. Drain and keep warm. Also at this time, preheat your broiler
Once the chicken is cooked, top each piece with spinach leaves and mozzarella cheese. Place oven-safe skillet in the broiler for a few minutes, until the cheese is melted and begins to brown.
Remove and serve chicken and sauce over the fettuccine noodles.