Thinly cut fresh basil into strips. Cut 8 ounces of fresh mozzarella into thick slices, and then shred ¼ cup fresh mozzarella. Set all aside.
Create a deep slit in each chicken breast. Place a thick slice of mozzarella in the chicken. Season with salt and pepper.
Put the flour, eggs and panko breadcrumbs into three separate coating trays. Add garlic powder, dried oregano, ¼cup Parmesan and ½ teaspoon salt to the panko bread crumbs, whisk well.
Dip the stuffed chicken first into the flour, then dip into the egg, turn to coat, then dredge in bread crumbs, making sure the chicken is evenly coated.
In a large skillet over medium heat, one tablespoon of olive oil. Add chicken to skillet and cook until golden on both sides, about 4 minutes per side. Pour marinara around chicken and scatter basil on top of marinara. Turn off heat then sprinkle remaining Parmesan and shredded mozzarella on top of chicken.
Transfer skillet to oven and bake until the chicken is cooked through, about 20 minutes more. Garnish with parsley if you like, and serve warm.