In a large (6 quart) slow cooker, place half of the crushed tomatoes, Italian seasoning, garlic, and salt. Place chicken breasts inside the slow cooker, top with half of the mozzarella and Parmesan cheese, and pour remaining crushed tomatoes on top.
Cover the slow cooker and cook, on low for 8 hours or 4 on high.
Meanwhile, heat broiler and line a baking sheet with foil. In a small bowl, combine panko breadcrumbs with olive oil and a pinch of salt and pepper. Spread in a thin, even layer on foil-lined baking sheet. Broil 3 to 5 minutes, stirring occasionally until breadcrumbs are evenly golden brown.
When chicken is cooked through, sprinkle remaining mozzarella cheese over top. Serve in bowls over pasta, if desired, topping the chicken with breadcrumbs and remaining Parmesan cheese.