Marinate the steak: Combine oil, soy sauce, wine, Worcestershire sauce, Dijon, lemon juice, garlic, Italian seasoning, and pepper in a large resealable bag. Squeeze the bag to blend ingredients.

Pierce flank steak with a knife, making small slits about 1 inch apart. Place steak in the bag, coat with the marinade, squeeze out excess air, and seal the bag. Marinate in the refrigerator for 8 hours to overnight.

When ready to cook, preheat the oven to 350 degrees F (175 degrees C).

Make the filling: Place crushed garlic onto a cutting board. Sprinkle salt over top and scrape with the flat side of a knife to make a paste.

Remove steak from marinade and shake off excess. Discard remaining marinade. Place steak onto a work surface and spread garlic paste all over the top side. Layer with chopped onion, bread crumbs, spinach, and feta. Starting at one of the short ends, roll steak lengthwise around the filling; secure with kitchen twine or toothpicks. Transfer to a shallow glass baking dish.

Bake, uncovered, in the preheated oven until the internal temperature of the roll is at least 145 degrees F (63 degrees F) in the center, about 1 hour.

Remove from the oven and let stand for 5 minutes so filling can set. Slice into 1-inch slices to serve.