Place an oiled frying pan over medium heat. While the pan is heating, cut a rectangle out of the bread. Fry the crust until golden brown. Meanwhile, cut the crumb into cubes.
As soon as a crust has formed, turn the bread over and beat in the egg, salt and add the crumb cubes.
Fry the egg for 2 minutes and turn over, sprinkle 2/3 of the cheese on top. Wait another 2 minutes and flip again.
Sprinkle the sandwich with the remaining cheese, after 30 seconds, turn over and fry for another 15-20 seconds.
Add vegetables for a balanced snack. If you like a runny yolk, fry not 2 minutes, but 1.5.