Preheat the oven to 375 degrees . Arrange the bacon on a broiler pan and bake until crisp, 15 to 18 minutes.
Meanwhile,preheat a cast-iron skillet or griddle over medium-high heat. Season the steak with the steak seasoning, if using (otherwise, use coarse salt and pepper), and drizzle with a little EVOO. Grill the meat, turning once, for 8 minutes for medium-rare. Remove from the heat and let rest, then thinly slice on an angle agains t the grain.
Using a food processor, pulse 1/3 cup EVOO, the chiles, shallot (or onion), garlic, cilantro, parsley, marjoram (or oregano), lime juice and vinegar into a chimichurri sauce. Season with salt and pepper.
To serve, arrange the sliced steak on the toast. Top with the watercress, bacon, tomato, lots of chimichurri and the remaining toast.