In a food processor, pulse the spinach, onions, and garlic. Add the cheeses, oregano, salt and pepper and pulse until just combined.
Butterfly the steak and open it like a book. The steak should be about 1/2 inch thick. Spread the spinach and cheese mixture to within about 1 inch of the edges. Roll up the steak jelly roll style and tie at 2 inch intervals with kitchen twine.
Add about 2 tablespoons of olive oil to an ovenproof saute pan over medium high heat. Saute the steak in the pan until brown on all sides, about 8 - 10 minutes.
Brush the steak with the A-1 Steak Sauce and transfer to the oven. Roast for about 15 minutes.
Turn the steak over, baste again with the sauce and roast an additional 10 minutes or until 125 - 130 degrees for medium rare. Remove from pan and place on a cutting board. Tent with foil and let rest for about 5 - 10 minutes.