Preheat oven to 400° F.
In a large mixing bowl, combine the beef, bread crumbs, minced onion, 1 tablespoon mustard, Worcestershire sauce, salt and pepper.
Gently press the beef mixture into a 13 X 9 inch pan so that it makes one large patty of even thickness.
Using the tines of a fork, poke holes throughout the meat.
Bake for 30 minutes. As it bakes, the meat will shrink away from the sides and fat will accumulate around the edges of pan.
When fully cooked, remove the pan from oven (keep oven turned on) and carefully drain off the liquid fat in the bottom of the pan or transfer beef onto a cookie sheet.
Top the meat patty with an even layer of sliced cheese; return to the oven for about 5 minutes and bake until the cheese is melted and bubbly.
Remove from the oven and allow to rest for a few minutes.
Cut meat into 12 squares or to fit the buns being used.
Serve with dill pickle slices, ketchup, mustard and/or your favorite burger sauce.