Place the chicken breast on a cutting board and using a sharp knife, cut each breast in half lengthwise (see notes) resulting in 4 chicken cutlets.
Season each side of the chicken breast cutlets with salt, pepper, and 1/2 teaspoon of Italian seasoning.
Add the avocado oil to a large oven proof skillet (such as cast iron or stainless steel) and heat over medium-high heat. Brown each side of the chicken cutlets and cook until a meat thermometer reads an internal temperature of 150F.
Remove the chicken from the pan to a plate and set aside. Pour the marinara in the skillet and scrape any browned bit from the bottom of the pan with a spatula. Return the chicken to the pan and top each cutlet with 1/4 cup of shredded mozzarella cheese, followed by the rest of the Italian seasoning.
Turn your oven on HI Broil and set the rack to the middle of the oven. Place the mozzarella chicken in the oven and broil until the cheese becomes browned and bubbly...about 5-8 minutes
Remove from the oven and check for proper chicken temperature of 165F using your meat thermometer. Serve.