1 big bundle watercress, upland cress or baby arugula
For the make-ahead sauce: In food processor bowl, combine the shallot, chile, garlic, bay leaves, mustard seed, sherry, Worcestershire sauce, and peppercorns, process into a smooth paste. Place the flavor paste in a pot and combine with the ketchup, soy, and stock. Bring the mixture to a boil, reduce the heat to a simmer and cook 30 minutes. Cool and refrigerate for make-ahead meal.
Preheat the oven to 325 degrees F to crisp the bread.
Reheat the sauce over medium-low heat.
Place the flank steak in the freezer 5 minutes or until cold. Remove and shred or cut the cold flank steak against the grain. Throw the bread in the oven to crisp it up. In a skillet, heat the high-temperature oil over high heat until it smokes. Add the meat and toss 2 minutes. Turn off the heat and combine with warm sauce. Cut the rolls open and stuff the hoagies with spicy greens and hot-n-saucy steak.