Combine the first five ingredients in a blender, then add parsley in small handfuls. Use a rubber spatula, spoon or butter knife to loosen and stir the leaves between blending them. Eventually, the sauce will be easier to blend; continue blending until it is smooth.
Add a pinch of salt if needed.
Lightly salt and pepper the steak. Grill for six minutes on each side for medium-rare. Let sit 5 minutes before slicing steak and mixing it with salad greens.
Serve chimichurri sauce drizzled over the salad.
