Stuffed Burgers

We had friends visiting not too long ago and one night for dinner they made these stuffed burgers. They took ground beef (I think it was 85% lean), mixed it with Worcestershire and seasoned salt, and then created somewhat thin patties using a disposable red cut to cut the patties into perfect circles. They then topped the patties with diced onions, pickles, and american cheese, and then sealed another patty on top, creating a stuffed burger. Grilled normally until cooked. These were truly incredible! There are so many possibilities of what you could stuff them with. I would like to try blue cheese sometime, or other kinds of cheese, and maybe jalapenos some time.