Combine first 6 ingredients in a bowl; stir well, and set aside.
Trim fat from steak. Using a sharp knife, cut horizontally through center of steak, cutting to, but not through, other side; open flat as you would a book. Place steak between 2 sheets of heavy-duty plastic wrap, and flatten to an even thickness, using a meat mallet or rolling pin. Spread spinach mixture over steak, leaving a 1-inch margin around outside edges. Roll up steak, jelly-roll fashion, starting with short side. Secure at 2-inch intervals with heavy string.
Coat a large Dutch oven with cooking spray, and place over medium-high heat until hot. Add steak, browning well on all sides. Add water, wine, and oregano to pan; bring to a boil. Cover, reduce heat, and simmer 1 hour or until tender. Remove string, and cut steak into 16 slices. Serve with cooking liquid and Feta Mashed Potatoes.