Prepare the Flank Steak

1. Place the flank steak on a cutting board. Use a meat mallet to pound it to an even thickness, about 1/4 inch.
2. Season both sides of the steak with salt and pepper to taste.

Spread the Pesto

1. Evenly spread the prepared pesto over the entire surface of the steak, ensuring full coverage for maximum flavor.

Layer the Fillings

1. Lay the thinly sliced prosciutto evenly over the pesto layer.
2. Sprinkle grated parmesan cheese over the prosciutto.
3. Arrange the baby spinach leaves evenly across the top.

Roll and Secure

1. Starting from one of the short ends, carefully roll the steak tightly to form a log.
2. Use kitchen twine to tie the steak roll at 1-2 inch intervals to secure it and keep the fillings intact during cooking.

Sear the Steak

1. Heat olive oil in a large skillet over medium-high heat.
2. Add the rolled steak to the skillet and sear on all sides until browned, about 2-3 minutes per side.

Bake to Perfection

1. Preheat your oven to 375°F (190°C).
2. Transfer the seared steak to a baking dish and place it in the oven.
3. Bake for 20-25 minutes, or until the internal temperature reaches 135°F for medium-rare or your preferred level of doneness.

Rest and Serve

1. Remove the steak from the oven and let it rest for 5-10 minutes.
2. Slice into 1-inch pinwheels, revealing the beautifully layered filling.
3. Serve immediately and enjoy!