Place coleslaw mix in a small bowl. Combine the sour cream, mayonnaise, horseradish sauce, mustard and salt. Pour over coleslaw mix and toss to coat.
Place bread slices on an ungreased baking sheet. Broil 4 in. from the heat until toasted, 2-3 minutes on each side. Layer with corned beef, coleslaw mixture and cheese. Broil 2-3 minutes longer or until cheese is melted.