Preheat oven to 350 degrees. Spray a casserole dish with non-stick cooking spray.
Spread the entire jar of spaghetti/marinara sauce on the bottom of the casserole dish.
In a small bowl, combine the panko crumbs, Parmesan Cheese, oregano, paprika, and pepper. Mix weill.
Dip one chicken breast into the melted butter, making sure it is fully coated.
Dip it again in the panko crumb mixture, making sure it is fully coated.
Place the chicken breast on top of the spaghetti sauce inside the casserole dish. Repeat steps 4 and 5 with the rest of the breasts. Sprinkle any left over panko crumbs on top of each breast in the casserole dish.
Bake for 45 minutes.
Sprinkle the shredded mozzarella cheese on top of the chicken and bake for another 10 to 15 minutes, until the cheese is melted and the chicken is tender and no longer pink inside.