Make meatloaf mix as per usual, sauteing the onion.  Flatten on wax paper.  Make a filling of mashed potatoes, an appropriate cheese for your flavour preference (we’ve had luck with both cheddar and parmesan) and appropriate spices for your chosen cheese.  Mushrooms can also be used.  Roll it up, and bake at 350 for 1 to 1 1/2 hours.