Heat the oven to 375°F (190°C). Place the flank steak on a cutting board and pat it dry. If it is thicker than about 1/2 inch (1.25 cm), carefully butterfly it by slicing horizontally through the thickest part, stopping before cutting all the way through. Open it like a book. Cover with plastic wrap and gently pound to an even 1/2-inch thickness.

Season both sides of the steak with the salt, pepper, oregano, and garlic powder. Position the steak with a long side facing you.

Spread the tomato sauce over the steak, leaving a 1-inch (2.5 cm) border around all edges. Arrange the ham over the sauce, then scatter 1 cup (113 g) of the mozzarella and the roasted red peppers on top.

Starting from the long side closest to you, roll the steak tightly into a log. Tuck in loose filling as you roll. Tie the roll crosswise with kitchen twine at 1 1/2-inch (4 cm) intervals, using 4 to 5 pieces of twine.

Heat the olive oil in a large oven-safe skillet over medium-high heat. Sear the steak roll for 2 to 3 minutes per side, turning carefully with tongs, until browned all around.

Transfer the skillet to the oven. Roast for 25 to 35 minutes, until an instant-read thermometer inserted into the center of the meat reaches at least 145°F (63°C). Sprinkle the remaining 1/2 cup (57 g) mozzarella over the top during the final 5 minutes of roasting.

Move the steak roll to a cutting board and rest it for 10 minutes. Remove and discard the twine. Slice into 1-inch (2.5 cm) rounds, sprinkle with parsley if desired, and serve warm.