Step 1: Prepare the Flank Steak: Place the flank steak on a cutting board and gently pound it to an even thickness of about 1/2 inch. This step tenderizes the meat and makes it easier to roll. Consider scoring the steak lightly in a crosshatch pattern to further tenderize and allow marinade (if using) to penetrate more effectively.
Step 2: Saut the Vegetables: Heat olive oil in a large skillet over medium heat. Add chopped onion and cook until softened, about 5 minutes. Add minced garlic and sliced mushrooms, cooking until the mushrooms are tender and have released their moisture, approximately 8-10 minutes.
Step 3: Wilt the Spinach: Add roughly chopped spinach to the skillet with the mushrooms and onions. Cook until the spinach has wilted, about 2-3 minutes. Remove the skillet from the heat and let the mixture cool slightly.
Step 4: Combine the Filling: In a mixing bowl, combine the cooked spinach mixture with ricotta cheese, Parmesan cheese, chopped sun-dried tomatoes, fresh basil, fresh oregano, salt, black pepper, and red pepper flakes (if using). Mix well to ensure all ingredients are evenly distributed.
Step 5: Stuff the Flank Steak: Spread the filling evenly over the prepared flank steak, leaving about 1 inch border along the edges.
Step 6: Roll and Secure: Carefully roll the flank steak tightly, starting from one end. Secure the roll with butcher's twine, tying it at 1-inch intervals, or use toothpicks to hold the seam together.
Step 7: Sear the Steak: Heat a tablespoon of olive oil in the same skillet over medium-high heat. Sear the rolled flank steak on all sides until nicely browned, about 2-3 minutes per side. Searing helps to lock in the juices and develop a flavorful crust.
Step 8: Bake the Steak (Optional): For a more evenly cooked steak, transfer the seared flank steak to a preheated oven at 375F (190C) and bake for about 20-25 minutes, or until the internal temperature reaches 135F (57C) for medium-rare or desired doneness. Alternatively, continue cooking in the skillet over low heat, covered, until the desired internal temperature is reached.
Step 9: Rest and Slice: Remove the flank steak from the oven or skillet and let it rest for at least 10 minutes before slicing. This allows the juices to redistribute, resulting in a more tender and flavorful steak. Remove the butcher's twine or toothpicks before slicing.
Step 10: Serve: Slice the stuffed flank steak into 1/2-inch thick slices and serve immediately.
Optional Tip: A marinade can be used for the flank steak before stuffing. Combine olive oil, balsamic vinegar, Worcestershire sauce, garlic, and herbs in a ziplock bag, add the flank steak, and marinate for at least 30 minutes or up to overnight in the refrigerator. Adjust the filling ingredients based on dietary restrictions or preferences, such as using gluten-free breadcrumbs instead of cheese.