Preheat the oven to 375 degrees. Lightly grease casserole dish. Set aside.
Season the diced chicken with salt, pepper, garlic and red pepper flakes.
Heat the oil in a fry pan and sear the chicken on both sides, making sure to only do a few pieces at a time to keep the chicken from steaming.
Mix Italian seasoning into marinara sauce and pour half the sauce into bottom of casserole dish. Add the chicken and top with remaining marinara sauce. Then add 1/2 cup of mozzarella and 1/2 cup of shredded parmesan over chicken.
In a small bowl, combine the panko, dried parsley, and butter. Sprinkle the panko on top of the cheese and then sprinkle the remaining cheese over panko crumbs.
Bake for approximately 25-30 minutes or until chicken is cooked through and the cheese is completely melted and golden on top.
Allow the dish to cool for approximately 5 minutes before serving. Enjoy!