What to do with sirloin?

My boyfriend's mom gave us a frozen piece of sirloin. It is not cut into steaks, which I am used to preparing, but instead looks like a roast or just a really thick steak, about 4 inches thick. Should this be slow cooked in a crock pot, seared and roasted, or some other method entirely? I am not sure how to treat this different cut of meat. Help!