Place the parsley, garlic, salt, pepper, pepper flakes, oregano, shallots, olive oil, sherry, and lemon juice, in a blender or food processor and pulse until well chopped well, but not pureed. Reserve.
Dissolve cayenne pepper and salt in 1 cup hot water. Transfer to a squeeze bottle container.
Place the steak directly over a hot grill, baste with the cayenne grilling sauce, and grill until the outer portion of the meat reaches the desired degree of doneness.
Remove the steak from the grill and slice long strips from the outer edges of the steak. Instruct guests to pick up a steak slice from the cutting board with their fingers, place it on a slice of baguette, and enjoy. Return the remaining steak to the grill, baste, and grill until more of the steak is cooked.
Remove and repeat the slicing and serving procedure until steak is consumed.
For extra spicy steak, baste 2 or 3 additional times during grilling process.
Serve the chimichurri sauce alongside the steak.