Preheat your oven to 375°F (190°C).

Lay the flank steak slices flat on a clean surface. If they are too thick, gently pound them with a meat mallet to about ¼ inch thickness.

In a mixing bowl, combine the Italian breadcrumbs, Parmesan cheese, chopped spinach, roasted red peppers, minced garlic, oregano, salt, and black pepper. Mix well until all ingredients are evenly incorporated.

Spread a generous amount of the breadcrumb mixture over each slice of flank steak, leaving a small border around the edges.

Sprinkle mozzarella cheese over the breadcrumb mixture.

Carefully roll up each slice of steak, starting from one end, and secure with toothpicks or kitchen twine.

In a large oven-safe skillet, heat the olive oil over medium-high heat. Once hot, add the steak rolls and sear on all sides until browned, about 3-4 minutes.

Pour the marinara sauce over the steak rolls and transfer the skillet to the preheated oven. Bake for 20-25 minutes, or until the steak is cooked through.

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