Peel and cut potatoes into 1/2-inch cubes Combine chicken and water in a large saucepan. Bring to a boil. Cover, reduce heat, and simmer 30 minutes or until chicken is tender.
Remove chicken, reserving broth. Bone chicken, and cut meat into bite-size pieces; set aside. Add potatoes, celery, and bouillon pwder to broth; bring to a boil. Cover, reduce heat, and simmer 15-20 minutes or until potatoes are tender.
Stir in mixed vegetables; set aside. Melt 2 T margarine in a heavy saucepan over low heat; add 2 T flour, stirring until smooth. Cook 1 minute, stirring constantly. Gradually add skim milk; cook over med heat, stirring constantly, until mixture is thickened and bubbly.
Remove from heat; stir in poultry seasoning. Combine reserved chicken, vegetable mixture, white sauce, and mushrooms in a large bowl. Spoon into individual baking dishes that have been coated with Pam.
CRUST: Combine 1 cup flour, baking powder, and salt in a small bowl. Cut in 1 T plus 1 1/2 t margarine with a pastry blender until mixture resembles coarse meal. Stir in buttermilk. Spoon biscuit dough into 6 portions over chicken mixture.
Bake at 350° F for 1 hour or until biscuits are golden.Servings: 6