Toast the bread until golden brown.
Wash the lettuce thoroughly and remove excess water.
Slice the tomato and onion thinly.
Lightly pan-fry the jambon ham or use as is.
Spread a thin layer of mayonnaise on the bread.
Layer the lettuce, tomato, onion, jambon ham, and Emmental cheese on the bread in order.
Top with another slice of bread to complete the sandwich.
Cut into bite-sized pieces and serve on a plate.