Preheat oven to 350°F. Lightly grease a 11×13″ baking dish.
Unroll one can of crescent rolls, seal the perforations to create a single sheet, then press into the bottom and up the sides of the dish as feasible. Bake for 20 minutes until the crust turns light golden. Remove and allow to cool slightly.
In a large skillet or saucepan, combine cooked chicken cubes, diced onion, peas and carrots, diced potatoes, condensed soup, water, poultry seasoning, salt, and pepper. Gently heat and stir over medium heat until warm and bubbly, adjusting water if the sauce feels too thick.
Pour the seasoned chicken and vegetable mixture over the cooled bottom crust in the baking dish. Evenly spread the filling.
Unroll the second can of crescent rolls, seal perforations into a sheet, and place it gently on top of the filling, pressing to touch the sides of the dish.
Bake for 25 minutes or until the top crust is golden. If necessary, loosely cover with foil if the crust browns too fast.
Remove from oven and allow the casserole to rest for 10 minutes before serving, letting the filling settle and making slices easier to serve.