Prepare the Marinade: In a bowl, whisk together olive oil, soy sauce, red wine, Worcestershire sauce, Dijon mustard, lemon juice, minced garlic, Italian seasoning, and black pepper.
Marinate the Steak: Place the pounded flank steak in a resealable bag and pour the marinade over it. Seal the bag and refrigerate for at least 8 hours or overnight, turning occasionally.
Preheat the Oven: Set the oven to 350°F (175°C).
Prepare the Steak: Remove the steak from the marinade and pat it dry. Discard the marinade.
Add the Filling: Spread the minced garlic over the steak, followed by chopped onion, bread crumbs, spinach, Swiss cheese, Parmesan, and sun-dried tomatoes.
Roll and Secure: Tightly roll up the steak from the short end and secure with kitchen twine or toothpicks.
Sear the Steak: Heat a skillet over medium-high heat and sear the steak roll on all sides until browned.
Bake to Perfection: Transfer the roll to a baking dish and bake for about 1 hour, or until a meat thermometer reads 145°F (63°C) for medium doneness.
Rest and Slice: Let the steak rest for 5-10 minutes before slicing into pinwheels. Serve warm and enjoy!