Melt butter in a large pot. Then add onions and carrots and cook until tender (about 5 minutes on medium heat).
Add in mushrooms and peas. Cook for an additional 2-3 minutes.
Then, add in the turkey, salt, pepper, parsley, and thyme and stir until well-blended. Pour in the gravy and heavy cream, stir, and cook on low heat for 5 minutes.
Transfer to a greased baking dish or ramekins. Top with leftover mashed potatoes (use a piping bag to achieve the look of our pie).
Mist with nonstick cooking spray. Place on a baking sheet and bake for 10-15 minutes until the potatoes are lightly browned and the filling is bubbly around the edges. (This may get messy, so clean up the edges before serving.)