Rolled and Stuffed Flank Steak with Spinach and Pecorino

This is a super easy meal that looks like it took eons to prepare. Also, you can prep the steak in advance and let it marinate up to 12 hours before cooking.

I chose to use Pecorino Romano cheese with the spinach, but another great cheese would be provolone!

Rolled Flank Steak with Spinach and Pecorino Romano
Note: If you want to serve a larger flank steak, (say 2 pounds instead of 1), just increase the bread crumbs and cheese slightly. There's no need to change anything else. 

1 flank steak, about 1 pound
Salt and freshly ground black pepper
1/2 cup Italian style seasoned bread crumbs
1/2 cup shredded Pecorino Romano cheese
1 cups baby spinach leaves
1 tablespoon balsamic vinegar
4 teaspoons olive oil, divided
1/2 teaspoon Dijon mustard

Preheat the oven to 350 degrees. 
Lay the steak on a flat surface with the horizontal lines parallel to you. Like this:  

Using a sharp knife, cut through horizontally, as if cutting a bagel, almost through to the other side, stopping about 1/2-inch from the opposite side. Open up the steak like a book. Like this: 

Season the steak with salt and pepper. 
In a small bowl, combine the bread crumbs and cheese. Sprinkle the mixture all over the steak. Arrange the spinach leaves all over the bread crumb mixture. Here's what it will look like: 

Starting from the shorter end, roll up tightly. Secure the steak evenly with 6 wooden picks. Like this: 

In a small bowl, whisk together the vinegar, 2 teaspoons of the oil and Dijon mustard. Brush the mixture all over the steak. At this point, you can marinate the steak (in the refrigerator) for up to 8 hours. 
Cut the steak crosswise into 6 equal pieces (each piece will be secured by the wooden pick). 
Heat the remaining 2 teaspoons of the olive oil in an oven-proof skillet over medium-high heat. Add the steak rolls and cook for 1 minute per side, just enough to sear until browned on both sides.  
Transfer the skillet to the oven and cook for 10 minutes for medium-rare, or about 15 for medium.
Let the steaks rest for 5 minutes before serving. 

Serves 4