Preheat oven to 400F.
Place the thawed spinach in the center of a kitchen towel. Holding the towel over the sink, twist it to squeeze excess water out of the spinach. Open the towel and place the spinach in a food processor.
Add the pine nuts, blue cheese and garlic to the food processor. Pulse until the ingredients form a thick paste about 10 seconds.
Arrange the steaks on a work surface. Use your fingers or a silicone spatula to spread a quarter of the cheese and spinach mixture in an even layer over each steak.
One at a time, roll the steaks into a cylinder. Use kitchen twine to tie each end of the rolls.
In a large, deep skillet over medium-high, heat the oil. Add the steak rolls and sear on one side for about 2 minutes. Use tongs to rotate the rolls slightly, searing for another 2 minutes. Continue until all sides are seared.
Transfer the rolls to a rimmed baking sheet and place in the oven to roast for 15 to 20 minutes, or until an instant read thermometer inserted in the center of the rolls reads 140° for medium. Rest several minutes before slicing and serving.
