Preheat oven to 425°F.

If you haven’t done so already, butterfly the steak by lining your knife up parallel to the cutting board and slicing through the center of the steak, stopping just before cutting it all the way through. Open up the flank steak up on the fold, doubling the original length.

Even out the thinness of the steak using a meat tenderizer so it’s about 1/2 inch thick. A little less thick is okay. Season with salt and pepper on both sides. Set aside on a large cutting board.

In a large, oven-safe skillet, like a cast-iron skillet, heat 1-2 tablespoons of olive oil over medium heat. Add the mushrooms and cook, stirring occasionally, for 5-7 minutes until softened and slightly browned. Add the garlic and cook for another 2 minutes until fragrant. Stir in the spinach then quickly remove from the heat. Spread mushroom and spinach mixture eevenly over the seasoned beef. Sprinkle with coat cheese if using.

Roll the steak with the grain (the lines in the meat), starting with the smallest end first. Roll the steak tightly, tucking in any loose pieces as you roll. Tuck the ends of the steak in to create an width along the whole roll.

Use cooking twine to snugly loop and tie the twine along the steak so its tight enough to hold it together. You can also use several toothpicks if you don’t have twine.

Add 1 more tablespoon of olive oil to oven-safe skillet and heat over high heat. When the oil starts to ripple, carefully place the rolled and stuffed flank steak in the pan and sear until the steak is browned on all sides, about 2 minutes on all four sides. Remove from the stove and place the skillet in the oven. Bake for 25 minutes or until a meat thermometer reads 135°F (medium rare) or reads to your desired doneness. Remove from the oven and allow to rest for 15 minutes before cutting. Cut into 2 inch medallions and serve hot.