Preheat the oven to 375°F.
In a medium bowl, combine the cream cheese, mozzarella cheese, Parmesan cheese, chopped spinach, minced garlic, salt, pepper, and Italian seasoning. Mix well until all ingredients are combined.
Lay the flank steak slices flat on a clean surface. Spread a thin layer of the cheese and spinach mixture evenly over each slice of steak.
Starting from one end, carefully roll each slice of steak tightly into a pinwheel shape. Secure the ends with toothpicks or tie with kitchen twine to hold the shape.
Heat olive oil in a large oven-safe skillet over medium-high heat. Add the pinwheels to the skillet and sear for about 2-3 minutes on each side until browned.
Transfer the skillet to the preheated oven and bake for 15-20 minutes, or until the steak reaches your desired level of doneness.
Remove from the oven and let the pinwheels rest for 5 minutes before slicing. Serve warm.