In a large mixing bowl mix the first 9 ingredients until well combined.
Butter a 9x9 baking dish. Spread meat mixture into pan. Or Make hamburger patties for the grill.
Mix the ketchup, vinegar, and brown sugar together and spread across the top of the meatloaf. If making hamburger patties- I would wait until the burgers are almost done and spread across the top of each patty.
Bake in a 350-degree oven for 25-30 minutes or until done.
To make hamburgers from the meatloaf cut out circles(or squares) and top with cheese of your choice. Grill for about 5 minutes or until cheese has melted.
Mix mayo and mustard together and spread on each hamburger bun. Add toppings of choice and enjoy!