Step 1

Pound the steaks with a meat mallet until about 2mm thick. Spray with oil and season with salt and pepper.

Step 2

Heat a frypan over high heat. Cook the steaks, 2 at a time, for 30 seconds each side for medium or until cooked to your liking. Rest for 3 minutes, then slice.

Step 3

Meanwhile, for the dressing, whisk ingredients with 1 tablespoon boiling water until combined. Season to taste.

Step 4

Fill the baguette pieces with tomato, watercress, onion, sliced steaks and any beef juices. Drizzle over the mustard dressing and serve immediately.