Preheat oven to 375°F. Pound flank steak to ½ inch thick between plastic wrap. Season with ½ tsp salt and ¼ tsp pepper.

Heat 1 tbsp oil in a skillet over medium heat. Wilt spinach for 2 minutes, add garlic, cook 30 seconds. Cool 5 minutes, then mix with feta, cream cheese, and sun-dried tomatoes.

Spread filling on the steak leaving a 1-inch border. Roll tightly from a short end and tie with twine at 2-inch intervals.

Season outside of roll with remaining salt and pepper. Heat remaining 1 tbsp oil in an oven-safe skillet over medium-high heat. Sear roll on all sides for 6 minutes. Roast in oven until internal temp reaches 125°F for medium-rare, 20 to 25 minutes.

Rest roll for 10 minutes. Remove twine, slice into 1-inch rounds, and serve with pan juices.