How to Make It
In a blender, combine all of the ingredients except the steak, salt and pepper. Puree until smooth. Put the steak in a large resealable plastic bag. Pour the marinade over the steak, seal the bag and turn to coat the meat. Refrigerate overnight.
Light a grill or preheat a grill pan. Pat the steak dry and season with salt and pepper. Grill over moderate heat until medium-rare, about 3 minutes per side. Transfer the steak to a cutting board and let rest for 10 minutes. Leave the grill on.
In a bowl, toss the shishitos with 1 tablespoon of the oil and season with salt and pepper. Grill the peppers until lightly charred all over, about 2 minutes. Grill the lemon halves cut side down until lightly charred, 5 minutes.
In a bowl, toss the grilled shishitos with the frisée, watercress, mint, celery and leaves and the remaining 2 tablespoons of olive oil. Squeeze 1 tablespoon of juice from a grilled lemon over the salad, season with salt and pepper and toss. Top with the cheese.
Thinly slice the steak across the grain. Serve with the salad and grilled lemon halves for squeezing over the steak.