In a medium bowl, mix together your leftover smoked turkey, vegetables, and gravy. Spread it into a small casserole dish.
In a separate medium bowl, re-season the mashed potatoes with salt and pepper as needed. Then mix in one egg. Layer this over the turkey mixture in the casserole dish.
Sprinkle the cheddar over the top of the mashed potatoes.
Cover and bake for 40 minutes. Uncover and bake an additional 10 minutes. Broil until the cheddar bubbles and browns.