To prep the steak, pat it thoroughly dry with paper towels. If the butcher hasn't removed the silver skin, gently lift it and cut it away. Refer to the video for visual cues.
Season steak on both sides with the salt and pepper.
Heat a 12-inch cast iron skillet on high for a few minutes. Pour in oil.
Add steak and let cook undisturbed for four minutes.
Flip once and continue cooking until internal temperature reaches 125°F for rare or 130°F for medium-rare.
Remove steak to a cutting board and let rest for 5 to 10 minutes.
Into a large bowl, place the arugula, romaine, red onion, and scallions. Pour in the dressing and toss to coat well.
Slice steak fairly thinly across the grain. (Refer to the video for visual cues.)
Place some dressed greens into each individual serving bowl and top with some sliced steak, hard-boiled egg, avocado, and blue cheese.
Drizzle steak with balsamic glaze and sprinkle with flaky sea salt and more scallions if you like.