Toast the bread, if desired. (I didn't toast, but you can if you prefer).
Spread mayonnaise over one side of each slice of bread.
On one of the slices of bread, layer on cheese (I used a 1.5 slices, basically enough to cover the slice of bread), roast beef, roasted peppers, red onion and Boston lettuce.
Top with the remaining slice of bread (with the mayonnaise side on the inside) to form the sandwich. Serve and enjoy!
