For the hamburger, chop the onion into very fine pieces and add to the ground beef in a mixing bowl. Combine the other hamburger ingredients together and mix until well incorporated. Patty hamburger into 6-8 patties, depending on the size of your buns. Place the hamburger patties on a hot grill and grill until cooked through and the center of the meat is no longer pink (about 6-8 minutes on each side). While the hamburgers are cooking, prepare the lettuce, slice the tomatoes, and cut the onion. For the train sauce, stir together the three ingredients and set aside. For the last few minutes of the burger cooking, place a slice of ham on top of the burger as well as a slice of cheese. Put the lid back on the grill and let the cheese and ham warm up. Once the cheese is melted, place the burger on the bottom bun. Top with some train sauce and your favorite hamburger fixings (lettuce, tomatoes, etc.).