Step 1: Butterfly or Flatten the Flank Steak

1. If your flank steak is not already butterflied, place it on a cutting board. Using a sharp knife, carefully slice the steak horizontally, stopping just short of cutting all the way through. Open the steak like a book.
2. Place a sheet of plastic wrap or parchment paper over the steak and pound it gently with a meat mallet until it’s an even thickness, about ¼ inch thick. This ensures even cooking and makes it easier to roll.

Step 2: Season the Steak

1. Season both sides of the steak evenly with salt and black pepper. Set it aside while you prepare the filling.

Step 3: Prepare the Filling

1. In a medium bowl, combine the chopped spinach, sun-dried tomatoes, mozzarella cheese, Parmesan cheese, breadcrumbs, minced garlic, Italian seasoning, and parsley. Mix well until all the ingredients are evenly combined.

Step 4: Assemble the Steak Roll

1. Spread the filling evenly over the prepared flank steak, leaving about a 1-inch border around the edges. This prevents the filling from spilling out as you roll the steak.
2. Starting from one of the short ends, carefully roll the steak tightly into a log. Tuck in any filling that tries to escape as you roll.
3. Once rolled, secure the steak with kitchen twine at 1-inch intervals to hold it together during cooking.

Step 5: Sear the Steak

1. Preheat a large oven-safe skillet or cast-iron pan over medium-high heat. Add 1 tablespoon of olive oil and heat until shimmering.
2. Place the rolled steak in the skillet seam-side down. Sear the steak for 2-3 minutes on each side until browned. This step locks in the juices and adds flavor.
3. Remove the skillet from the heat.

Step 6: Add the Sauce

1. Pour the marinara sauce over and around the steak in the skillet. If desired, thin the sauce with ½ cup of beef or chicken broth for a lighter consistency.
2. Spoon some of the sauce over the top of the steak roll to keep it moist during baking.

Step 7: Bake the Steak

1. Preheat your oven to 375°F (190°C).
2. Transfer the skillet to the oven and bake for 25-30 minutes, or until the internal temperature of the steak reaches 130-135°F (55-57°C) for medium-rare, or 140°F (60°C) for medium. Use a meat thermometer for accuracy.
3. Baste the steak with the sauce once or twice during baking to keep it moist and flavorful.

Step 8: Rest and Slice

1. Remove the steak from the oven and let it rest for 10 minutes. Resting allows the juices to redistribute and makes slicing easier.
2. Carefully cut the twine and discard it. Using a sharp knife, slice the steak into 1-inch-thick rounds to reveal the pinwheel filling.

Step 9: Serve and Garnish

1. Arrange the sliced steak on a serving platter and spoon the sauce over the top.
2. Garnish with fresh parsley and extra Parmesan cheese, if desired. Serve immediately with your favorite side dishes.