Combine the ground beef, steak seasoning, and Worcestershire sauce and form them into patties.
When the skillet is hot enough, add half of the butter, then add the patties and cook for 2-3 minutes on each side.
Once the burgers are cooked, place 2 slices of Swiss cheese on top of each patty and cover the skillet with a lid to let the cheese melt.
While the burgers are cooking, in a separate pan, sauté the sliced mushrooms and onions in the remaining butter until they become tender and caramelized.
Assemble the homemade burgers by placing the beef patties on the hamburger buns and top them with the sautéed mushrooms and onions.