Shared by Treva with recipegoldmine.com

2-3 cups turkey (or you could use chicken, ham or beef -
    whatever you have left over)
1 to 2 cups gravy
2 cups mashed potatoes
1 (12 ounce) bag mixed vegetables (or any kind you prefer),
    OR left over veggies from your dinner
Leftover stuffing, if you have it, or use your favorite
    stuffing recipe, enough to top the casserole

Heat oven to 350 degrees F.

In a 9 x 13-inch pan or large oven-safe casserole dish (or whichever size is appropriate if you don't have as many leftovers), spread the mashed potatoes in the bottom of the pan, layer meat and vegetables over the potatoes. Spread gravy over the top, then top with leftover stuffing. If you don't have stuffing leftover, or don't care for it, you can put the mashed potatoes on top of the casserole to make a crust. Bake for approximately 30 minutes or until hot.

Serves 4-8, depending on the size of their appetites. The smaller size casserole will serve fewer people.