Pat the steak completely dry and season it generously with salt and pepper on both sides.
Sear it in a very hot pan for 3 to 4 minutes per side for medium-rare, without moving it.
Rest the steak on a board for a full 10 minutes. Do not cut it early.
While it rests, whisk the red wine vinegar, Dijon mustard and black pepper together, then whisk in the olive oil.
Toss the arugula, cherry tomatoes and red onion with the vinaigrette.
Slice the steak thinly against the grain at a 45-degree angle, lay it over the dressed leaves, and scatter the blue cheese over the top.