Oh Snap Macros

In a small bowl, whisk together the olive oil, coconut aminos, minced garlic, brown sugar, Worcestershire sauce, balsamic vinegar, dried rosemary, salt, and black pepper to create the marinade.
Place the flank steak in a large resealable plastic bag or shallow dish. Pour the marinade over the steak, ensuring that it is well-coated. Seal the bag or cover the dish and refrigerate for at least 1 hour, or up to 2 hours for a more intense flavor. Overnight is always best. 
Preheat the oven to 400 degrees Fahrenheit. Remove the flank steak from the marinade, discarding the excess marinade, and let the steak rest at room temperature for about 15 minutes before cooking. The discarded marinade has been accounted for in the nutrition facts.
In a large cast iron skillet, heat the olive oil over medium-high heat until it begins to shimmer. Carefully place the flank steak in the hot skillet and sear each side for 2 minutes, or until a golden brown crust forms.
Transfer the cast iron skillet with the seared flank steak to the preheated oven. Cook the steak for 5-10 minutes, or until the internal temperature reaches your desired level of doneness (125°F / 51°C for medium-rare, 135°F / 57°C for medium). I recommend medium rare, which is about 5 minutes in the oven.
Remove the skillet from the oven and transfer the flank steak to a cutting board. Tent the steak with aluminum foil and let it rest for 5-10 minutes to allow the juices to redistribute.
After resting, slice the cast iron flank steak against the grain into thin strips.