Sort the salad, wash and drain. Dab meat dry. Fry half of it in 1 tbsp. oil for approx. 1 minute. Turn, sprinkle with half of the cheese and fry covered for about 2 more minutes. Repeat with 1 tbsp. oil, rest meat and cheese.
Peel onions and cut them into rings. Heat 1 tablespoon of oil in the frying fat, fry the onions until soft. Caramelise with 1 tbsp. sugar, deglaze with vinegar.
Cut bread open and quarter it. Brush lower halves with mustard. Cover with salad, meat and onions. Place the upper halves on top.