Pour all veggies into the pie crust.
Now, if for some reason you don't want an adorable pie, you can simply top with the remaining mashed potatoes and bake. Otherwise...
Fill a decorator thingy or pastry bag with mashed potatoes
Using a large star tip, begin outlining the body with stars
Fill in the circle, leaving the area for the head empty, except for the eyes
Switch to the dyed potato and a circle pastry tip to fill in the rest of the face, eyes and feet.
Bake at 350o
C until lightly browned, about 30 minutes.