1) Mix the Worcestershire sauce, olive oil, hot sauce, and 5 cloves of chopped garlic in a large glass baking dish. Add the steak and swish around, turning until evenly coated.
2) Marinate at room temperature for 15 to 30 minutes, or cover and refrigerate for up to 4 hours, flipping the steak once or twice.
3) Preheat an outdoor barbecue or griddle pan to medium to medium-high heat.
4) Remove the steak from the marinade and season 1 side with salt and pepper. Place seasoned side of the meat down on the barbecue or the griddle. Cook the steak undisturbed for 5 minutes. Then rotate the meat about 90 degrees (don't turn it over) on the barbecue or griddle to make clear cross marks and cook for another 2 minutes.
5) Season the other side of the steak with salt and pepper and flip. Continue to cook until an instant-read thermometer registers 60C for medium, about 8 to 10 minutes. Transfer to a cutting board to rest for 15 minutes.
For the onions:
1) Meanwhile, heat a large pan over medium-high heat, add the olive oil and when shimmering add the onions. Cook, stirring occasionally; until the onions are brown, about 8 minutes.
2) Then stir in the garlic, salt, thyme, and hot sauce, cook until onions are tender, about 4 minutes. Add the broth and scrape up any browned bits from the bottom of the pan. Cook until all the chicken broth is gone, and then season with pepper. Set aside.
For the blue cheese sauce:
Mash the blue cheese in a bowl with the mayonnaise or sour cream, lemon zest, and pepper to taste. Set aside.
For the roasted tomatoes:
1) Preheat the oven to 210C/Gas Mark 7.
2) Toss the tomatoes in a large bowl with the olive oil, thyme, garlic, salt and pepper. Transfer to a baking tin cut side up and roast until soft and juicy, about 20 minutes.
To assemble the sandwiches:
1) Cut the rolls in half horizontally and brush the insides with olive oil. Barbecue or griddle until warm on each side, about 1 minute.
2) Rub the toasted bread with the remaining clove of garlic.
3) Thinly slice the meat across the grain and assemble the sandwiches. Spread a few tablespoons of the blue cheese sauce on each sandwich, top with some of the steak, onions, roasted tomatoes and watercress.
4) Serve warm or at room temperature.