Preheat oven to 375ᵒ F.
In a skillet, sauté onion in vegetable oil until golden. Add mushrooms and celery and sauté briefly. Set aside.
In a large mixing bowl, hydrate the stuffing according to package instructions, using amounts of water and vegetable oil (or butter) indicated.
Stir sautéed vegetables into stuffing. Adjust seasonings and add nuts.
Turn stuffing into a greased 2- to 3-quart casserole or 9 x 13-inch baking pan. Cover and bake for 30 to 45 minutes. For a drier dressing with a crisp top, bake uncovered.
Note: If the size of your stuffing package is more than 8 ounces, simply adapt the recipe accordingly.