This page is dedicated to Car Wash Mike, who has inspired the forum with many of his fabulous BGE creations, not the least of which is the infamous Onion Burger.
Using his basic principle, I kicked it up a notch. First, I started with really good ground beef - actually, my dad got this stuff at Publix and basically what they do is grind up all of the trimmings from all of the cuts of beef they have sold that day. Basically, you're getting some sirloin, tenderloin, ribeye, and lots of good beef in there. Alternatively, you can also ask the butcher to grind you up a brisket flat, which also makes delicious hamburger meat.
I formed the burgers into 1" thick patties, about 1/3 pound per burger, and seasoned with kosher salt and freshly ground black pepper (you could also use Dizzy Pig's Raisin' the Steaks rub or Cow Lick rub). Then I dug out a little pool in the center and pushed in some fresh goat cheese (you could also use bleu cheese), then sort of covered it up with the beef (but not all the way). I then added the Car Wash Mike touch and pressed a fresh slice of a white onion in the center. I sort of folded the burger around the edges of the onion to keep it in place. Finally, add some butter, pepper, and salt on top of the onion.