Preheat the oven to 350°F (175°C) and grease a 1.5-quart baking dish.

Boil salted water in a large pot, then add jumbo pasta shells and cook for approximately 8-9 minutes until al dente. Drain and cool.

In a mixing bowl, combine shredded turkey, warm mashed potatoes, diced celery, chopped onion, minced garlic, and half of the cheddar cheese. Season with salt and pepper.

Pour ¾ cup of gravy into the bottom of the greased baking dish.

Stuff each pasta shell with the filling and arrange them seam-side up in the baking dish.

Drizzle remaining gravy over the stuffed shells and sprinkle with remaining cheddar cheese.

Bake in the preheated oven for 25-30 minutes until bubbly and golden brown.

Let the dish cool for a few minutes before serving.