Preheat oven to 375

In a large pan, heat olive oil on medium-high heat and sauté onions, carrots, and celery until onions are translucent and carrots and celery are tender.

Stir in cooked turkey, garlic, corn, peas, and gravy and continue cooking until heated through and bubbly.

Pour mixture into an 8x11 baking dish and top with mashed potatoes. Spread mashed potatoes evenly to cover casserole.

Bake for 25-30 minutes or until potatoes are cooked through and golden and casserole is bubbly.