Start by butterflying the flank steak if it isn’t already. Lay it flat on your cutting board, and using a meat mallet, gently pound the steak to an even thickness.
In a skillet over medium heat, add the oil. Once hot, toss in the chopped onion and sauté until they become translucent, about 5 minutes. Add the minced garlic and sauté for an additional minute until fragrant. Stir in the baby spinach and cook until wilted, around 2-3 minutes. Remove from heat and allow the mixture to cool slightly.
In a mixing bowl, combine the cream cheese and half of the Provolone cheese with the sautéed spinach mixture. Season with salt and pepper to taste.
Lay the butterflied flank steak on a clean surface, and spread the spinach and cheese filling evenly over the top. Leave a small border around the edges to prevent the filling from spilling out when rolled. Sprinkle the remaining Provolone cheese on top of the filling.
Starting from one end, roll the flank steak tightly around the filling. Use cooking twine or toothpicks to secure the rolls at intervals.
Preheat your oven to 375°F (190°C). Place the stuffed flank steak rolls in a baking dish, seam side down. Bake for about 25-30 minutes, or until the meat reaches your desired doneness.
