Preheat grill to medium-high heat. Place a large skillet with a 1/4 inch of water on to boil. Brush the steaks with 1 Tbsp of the olive oil; season generously with salt and pepper. Grill to desired doneness over medium-high heat. (Allow 2-3 minutes per side for rare, 3-4 for medium rare, and 4-5 for medium). While this occurs, place the spinach in water and cook until just wilted. Drain excess water from spinach, then season with salt and pepper. Serve steaks on a bed of spinach, drizzle with remaining olive oil, sprinkle with parsley and lemon zest, and serve.