In a greased 3-qt. slow cooker, combine chicken, salsa and taco seasoning. Cook, covered, on low until chicken is tender, 4-5 hours., To serve, preheat broiler. Shred chicken with 2 forks; stir in tomatoes and cilantro., Place bread on ungreased baking sheets; broil 2-3 in. from heat until tops are lightly browned. Using tongs, place rounded 1/3 cup chicken mixture on each toast. Sprinkle with cheese. Broil until cheese is melted, 2-3 minutes. If desired, top with olives and additional tomatoes. Freeze option: Cool chicken mixture without tomatoes and cilantro; freeze in freezer containers. To use, partially thaw in refrigerator overnight. Heat through in a saucepan, stirring occasionally; stir in tomatoes and cilantro and serve as directed.