Slice roll horizontally into 3 layers. Scoop out bottom roll slice, leaving a 1/4-inch shell.
Combine mayonnaise, green onion, and mustard. Mix well.
To serve, spread bottom roll slice with half of the mayonnaise mixture. Top with a lettuce leaf. Spoon coleslaw onto lettuce-lined roll. Top with the tomato slices.
Place middle slice of roll over tomato slices. Spread with remaining mayonnaise mixture. Arrange pastrami and Swiss cheese over mayonnaise. Top with remaining roll slice. Makes 1 sandwich.