Preheat your oven to 350°F (175°C).

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

Lay the thinly sliced flank steak on a clean surface. Place a generous amount of the cheese and spinach mixture at one end of each slice.

Roll the steak tightly around the filling, securing it with kitchen twine or toothpicks to hold the shape.

In a large oven-safe skillet, heat the olive oil over medium heat. Add the stuffed braciole and sear on all sides until browned, about 5 minutes.

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 30-35 minutes, or until the steak is tender and cooked through.

Remove from the oven and let it rest for 5 minutes before slicing. Garnish with fresh basil leaves before serving.