Make the marinade. In a shallow baking dish, combine the olive oil, lemon zest, juice, garlic, red pepper flakes, rosemary, oregano, salt and pepper and stir well. Pat the steaks dry and place them in the marinade and turn them so they’re completely coated in the marinade. Cover with plastic wrap and refrigerate for at least 8 hours, up to 48 hours.
Prep the steak for grilling. 30 minutes before cooking, remove the steaks from the fridge so they can come to room temperature. Remove the steaks from the marinade and shake off any excess. Give the outsides of the steaks a sprinkle of salt and pepper.
Prep and preheat the grill. Preheat an outdoor grill over medium heat to 500 F. Let the grill preheat for a full 15 minutes. Make sure the grates are cleaned of any debris and lightly grease them with oil or nonstick cooking spray. Right before you cook the steaks, increase the heat to medium high.
Grill the steaks. Lay the steaks diagonally across the grates of the grill (don’t close the lid) and let them sear for 3-4 minutes. Rotate them 90 degrees clockwise and let them sear for another 2-3 minutes so you get a nice crosshatch pattern. While the steaks are grilling, grill the lemons cut side down for 4-5 minutes. Flip the steaks, turn off the heat, close the grill lid, and let them cook for 4-6 minutes, or until the internal temperature registers at around 130 F.
Rest & Slice. Remove the steaks and lemon from the grill and let the steaks rest for 10-15 minutes before slicing. Sprinkle the sliced steak with flaky sea salt and a squeeze of the grilled lemons.