Peel the onion and cut into very thin slices. Cover with the frozen beans and cook in boiling salted water for about 10 minutes. Clean the mushrooms, wash them briefly if necessary. Wash the rosemary, shake dry and pluck the needles.
Pat the steaks dry. Heat oil in a pan. Fry the steaks in it for 1-2 minutes on each side, then fry them over medium heat for a pink steak (medium).
Continue frying for 3-4 minutes. Season with salt and pepper. Take out and let it rest for about 5 minutes wrapped in aluminium foil.
Fry the mushrooms in a hot frying pan for 2-3 minutes until golden brown. Add rosemary. Deglaze with vinegar and 2-3 tbsp. water, bring to the boil, simmer for 1-2 minutes. Season to taste with salt and pepper.
Drain the beans well. Arrange steaks with balsamic mushrooms and beans. Add ciabatta.