Grease a frying pan with cooking oil. Fry the Spam for 2 minutes per side. Set aside.
Place the bread slices in a toaster. Toast for 2 minutes.
Spread the mayonnaise on one side of each bread slice. Set one bread slice on a plate – side with mayonnaise facing up. Put the American cheese followed by the Spam and egg. Top with the remaining bread slice – side with mayonnaise facing down.