1. Heat a charcoal or gas grill until hot (you should barely be able to hold your hand 3 or 4 inches from the fire), or use a grill pan or medium-sized skillet on medium-high heat. Meanwhile, bring the steak to room temperature, pat it dry with paper towels, and sprinkle both sides with salt and pepper.
2. Grill or broil steak until nicely browned, 3 to 4 minutes per side. Move the meat to a cooler part of the grill and cook another 5 to 7 minutes, turning once
3. While the steak cooks, put the olive oil in a 12-inch skillet over medium-high heat. When its hot, add the greens, and sprinkle with tsp. each salt and freshly ground pepper. Cook, tossing frequently.
4. Cover steak and let rest for 5 minutes before cutting across the grain into thin slices. Serve with greens.