In a large saute pan, add one tablespoon of olive oil (or just a good swirl of the pan). Add minced garlic and sliced shallot, allowing to saute until fragrant, about 1 minute. Add spinach and continue to cook until wilted. Remove from heat to allow to sightly cool.
Meanwhile, butterfly the steak. Place flank steak on a cutting board, and using a very sharp knife, slice the steak horizontally, but stopping before you get all the way through. You'll be opening this piece of meat up to double its size. Place a piece of plastic wrap over the meat, and using a meat mallet, pound the steak out to a uniform thickness, until about 1/4 inch thick.
With the long end of the steak closest to you, layer the sautéed spinach and shallots, followed by the blue cheese on top of the steak. Working from the end closest to you, begin rolling the steak up, eventually securing it with kitchen twine.
Add 1 tablespoon of olive oil to the large saute pan. Add steak roll up, searing on all sides. If you prefer your steak rare, you'll need a few minutes on each side until it's done. For medium rare to medium, with the cheese melted, add to a 400 degree oven for about 10 minutes. Remove from heat and allow to cool slightly before slicing into medallions to serve.