Stir together first 8 ingredients. Tear tortillas into 1-inch pieces; layer one-third of tortilla pieces in a lightly greased 6-qt. slow cooker. Top with one-third of chicken mixture and 2/3 cup cheese. Repeat layers twice.
Cover and cook on LOW 3 1/2 hours or until bubbly and edges are golden brown. Uncover and cook on LOW 30 minutes.