Whisk together the yogurt, cumin, lime zest, and ¼ teaspoon each salt and pepper in a small bowl; set aside.
Thinly slice the cauliflower, starting with the crown and working down to the stem end.
Toss together the cauliflower, scallions, pecorino, lime juice, 3 tablespoons of the oil, and ¼ teaspoon each salt and pepper in a medium bowl.
Heat the remaining tablespoon of oil in a large skillet over medium-high heat. Season the steak with ½ teaspoon salt and ¼ teaspoon pepper.
Cook, 3 to 4 minutes per side for medium-rare. Let rest for 5 minutes before slicing against the grain.
Serve the steak with the cauliflower salad and cumin-lime yogurt.