Preheat your oven to 350°F.

In a mixing bowl, combine the chopped spinach, ricotta cheese, Parmesan cheese, breadcrumbs, minced garlic, oregano, salt, and black pepper. Mix until well combined.

Lay the pounded flank steak flat on a clean surface. Spread the cheese and spinach mixture evenly over the steak, leaving a small border around the edges.

Starting from one end, carefully roll the steak tightly into a log shape. Use kitchen twine to tie the roll at 2-inch intervals to secure it.

In a large oven-safe skillet, heat the olive oil over medium-high heat. Sear the beef braciole on all sides until browned, about 3-4 minutes per side.

Pour the marinara sauce over the braciole in the skillet. Cover the skillet with a lid or aluminum foil and transfer it to the preheated oven. Bake for 45 minutes to 1 hour, or until the beef is tender.

Remove from the oven and let it rest for 10 minutes before slicing. Garnish with fresh basil leaves before serving.