In a bowl, combine the beef, ground oatmeal, salt, pepper, minced onions and optional minced mushrooms. Use your hands to combine thoroughly.
Form the mixture into 6-8 patties.
Heat a large heavy frying pan on medium-high heat. Cook the patties, in batches if necessary, flipping once, until no longer pink in the middle.
Place in the buns with lettuce, tomato, and any toppings.
