In small mixing bowl, flake crabmeat.
Add mayonnaise, mustard, Worcestershire sauce and horseradish; mix well.
Cut each slice bread into 4 squares.
Arrange on 2 napkin-lined plates or trays.
Top each with about 1 teaspoon crab mixture; sprinkle with Parmesan cheese.
Cook 1 plate at a time, uncovered, 1 minute or until edges of filling begin to bubble