Microwave margarine uncovered in custard cup on high (100%0 until softened, 15 to 30 seconds. Blend in mustard. Spread margarine on one side of each toast lsice. Place slices buttered sides up on serving plate; top with ham tomato and cheese slices.

Microwave uncovered until cheese begins to melt, 1 1/2 to 2 minutes. Top each sandwich with a spoonful of coleslaw.