Preheat the oven to 350 degrees F (175 degrees C).
Put the spinach, sun-dried tomatoes, garlic, lemon, and pine nuts in a food processor and process until minced.
Drizzle in 1 or 2 tablespoons of the oil until you end up with a pesto consistency.
Cover the meat with plastic wrap and pound with a meat tenderizer to make it 1/4-inch (3/4-cm) thick.
Grind some salt and pepper over the meat.
Use a spatula to spread the pesto mixture over the meat, leaving a 1/2-inch (1 1/4-cm) border.
Following the grain, roll the meat up and use kitchen twine to wrap it in 3 places tightly.
Heat a tablespoon of oil in a skillet on the stove.
Brown the rolled up flank steak for a couple of minutes per side.
Put the skillet in the oven and roast for 25 minutes for a medium result.
Let the stuffed flank steak rest for 5 minutes, and then slice and serve.