Preheat oven: Set oven to 375°F (190°C). Grease a 9×13-inch baking dish.
Prepare sauce base: In a mixing bowl, whisk together cream of mushroom (or gravy) and milk until smooth. Season lightly with salt and pepper.
Layer casserole:
Spread shredded turkey evenly in the bottom of the dish.
Scatter mixed vegetables over the turkey.
Pour sauce mixture evenly over the top.
Sprinkle shredded cheese across the surface.
Add stuffing layer: Spread stuffing evenly on top, gently pressing down with a spoon to form a light crust.
Optional topping: Mix breadcrumbs, Parmesan, and melted butter, then sprinkle over stuffing for extra crunch.
Bake: Place in the oven uncovered for 30–35 minutes, until stuffing is golden brown, cheese is melted, and casserole is bubbling.
Rest & serve: Allow to sit for 5 minutes before serving. The aroma of toasted stuffing and melted cheese will make it irresistible!