Clean the tomatoes, cut eighths, cut into 3 pieces each. Peel the onion, cut in half and cut into strips.
Heat 1 tablespoon of oil in a grill pan. First grill 2 steaks on each side for approx. 3 - 4 minutes, season with salt and pepper and set aside. Do the same with the other steaks. Let the 4 steaks rest in a warm place for about 5 minutes.
In the meantime, mix the vinegar with salt and pepper and beat the olive oil on top. Add tomatoes and onion.
Serve the steaks with tomato salad and herb butter florets. Garnish with parsley.