Season the steaks generously with celery salt and drizzle with half the oil, then set aside.
Fry the onions, leek, garlic and thyme in the remaining oil for 5 minutes, until softened. Add the eggplant, tomatoes, potatoes and zucchini, then cook for 20 minutes, until thickened. Season with salt and pepper, then mix in the green beans and parsley.
Cook the steaks on a hot ribbed griddle for 8 minutes turning several times, until medium rare. Rest, then serve with tomato ragu and flatbread.