Put the watercress, grapefruit and fennel into a large bowl and season with salt and pepper, to taste. Add the lemon juice and the olive oil and toss to combine.
For the brisket:
In a small saute pan, add the BBQ sauce and brisket, and cook over medium heat until beef is hot and cooked through. Top the brisket with 3 slices of Cheddar and toss together until combined. Season with salt and pepper, to taste.
Put the brisket on the toasted brioche bun and serve with the watercress salad.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.