Use basil, lemon or rosemary oil instead of olive oil. Replace the caramelised onions with a few roasted peppers from a jar.
Put the grill on. Heat a little oil in a frying pan. Season both sides of the steaks with salt, then fry for 1-2 minutes on each side. Meanwhile, slice the ciabatta in half lengthways and grill the cut sides until golden.
Drizzle the toasted ciabatta with olive oil, spread the bottom half with the onions and sit the steaks on top. Cover with the watercress and close the sandwich with the other half of the ciabatta. Cut into four sandwiches and serve two per person. Serve hot.