Use the leftovers from a roast beef, and place them in the bottom of a baking dish (the size depends on how much leftovers you have, how many people you're feeding, etc.).
Make mashed potatoes (again you must judge how much you'll need) and place them directly on top of the beef. Bake in the oven for about hour at 350 degrees, just until warmed through. You can dot the top of the potatoes with butter for a golden finish.
Fry about 2 lbs. of hamburger with 1 chopped onion. Place in baking dish. Make or use leftover mashed potatoes and place them on top of the hamburger. Bake for hour at 350 degrees, just until warmed through. Serve with gravy.
Tailor it to your taste and let me know how it comes out. It's pretty simple and doesn't take too much prep time, especially if you happen to have a lot of mashed potatoes leftover.
For singles, it's good to know that the hamburger version freezes well. I have made a pan (layered hamburger, cream-style corn, mashed potatos) then frozen sectons in microwavable dishes and can just pop them into the microwave after a long day at work. Or, if I think about it before, put one in the refrigerator for baking when I get home.
Try using a taco seasoning with the hamburger, or other favorite meat seasonings, it certainly gives it a different favor.
When using meat seasonings, add vegetables or other ingredients that compliment that seasoning, i.e. snow peas when using teryaki sauce, shredded cheddar cheese when using the taco seasoning.
Add grated cheese to the mashed potatos.