Arrange chicken in slow cooker and season with salt pepper, and italian seasoning. Sprinkle pepperoni and olives over chicken and pour the UNdrained diced tomatoes over the top of everything.
Cook 6 hours on low or 3-4 hours on high or until the chicken is tender.
Remove lid and sprinkle mozzarella cheese over the top of the chicken. Replace lid just long enough to melt cheese and serve.