Preheat the oven to 400 degrees F (200 degrees C). Add olive oil to the bottom of a small, shallow baking dish, and sprinkle chili flakes over the oil.
Place chicken breast in the prepared dish, and season both sides with salt and pepper. Finish with the smooth side of chicken breast facing up.
Spoon marinara sauce over chicken breast, covering it completely.
Top marinara sauce evenly with half the mozzarella and half the Parmesan cheese. Scatter croutons evenly over cheese, breaking about half of them to get a variety of sized pieces. If croutons are very small, place them on as is.
Cover croutons evenly with remaining mozzarella and Parmesan.
Bake in the preheated oven until an instant-read thermometer inserted into the thickest part of the chicken registers 165 degrees F (74 degrees C), 30 to 35 minutes. Exact time will vary based on the size of the chicken breast.
Let rest at least 5 minutes before serving. Garnish with freshly chopped Italian parsley.
