I'd sear the stuffed and rolled roast in pan and finish it in the oven until it's medium rare. Then I'd make a gravy in the pan to serve with it.
Pounded flank steak is very thin and will cook quickly. Because of the nature of this cut, it becomes shoe leather if it's overcooked. You should keep it to the rare side of medium. To accomplish this and not be stuck with cold stuffing, I stuff the roast with stuffing that's already hot then cook it immediately.
If you are going to stuff it ahead of time, don't do this.
Be sure to roll the stuffed roast so the grain of the meat runs the length of the roast rather than around the circumference. That way, when you slice it, you will be slicing across the grain, which results in a more tender meat.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan