To a small jar, add extra-virgin olive oil, lemon juice, garlic, cumin and sumac. Secure the lid on the jar, and shake until the marinade/dressing is well combined. Spoon half of the marinade/dressing over both sides of the steak (reserve the rest for the salad that goes on top). Season both sides of the steak generously with kosher salt and black pepper. Let the steak sit at room temperature for 30 minutes (or in the refrigerator overnight).

Preheat your broiler to high. Take the steak from the marinade and lay it flat on a rimmed baking sheet. Broil for 5 minutes on one side, then flip and broil for 4 to 5 minutes more. Timing will depend on personal preference (how rare you like it) and thickness of steak. I like my steak rare. Overcooked flank steak is very tough and chewy.

Transfer the steak to a cutting board and let rest for 10 minutes. In a bowl, combine the arugula, green onion, and parsley, and drizzle the reserved dressing over the top. Toss to combine. Season to taste with kosher salt and black pepper.

Slice the steak against the grain (this will keep your steak from being chewy), and arrange on a large cutting board or platter. Season steak with a little kosher salt. Top the steak with the arugula salad, then dot the plate with crumbled feta.