Preheat oven to 350°. In a large saucepan combine butter and mustard over medium heat. Stir in contents of produce stuffing kit; cook until veggies are tender. Add water chestnuts, walnuts, poultry seasoning and pepper. Toss with dressing mix and chicken broth. Place stuffing in a 6 quart casserole dish and bake for 30 minutes in preheated oven.